Chapter -1.5 "Forces" - Long Questions

 Chapter -1.5  "Forces"

Question 1

A student stretches a rubber band and then releases it.

(a) Define a force. [2]

(b) State what is meant by deformation. [2]

(c) Explain why the rubber band becomes longer when stretched. [3]

(d) Explain why it returns to its original length after being released. [3]

Answer 

(a) A force is a push or a pull that can change the motion, size, or shape of an object.

(b) Deformation is a change in the size or shape of an object caused by a force.

(c) When the rubber band is stretched, a tension force pulls its particles further apart. This increases its length and decreases its thickness.

(d) The force applied is within the elastic limit. The particles remain bonded and return to their original positions when the force is removed. This is elastic deformation.

Question 2

A metal spring is compressed between two hands.

(a) Name the type of force acting on the spring. [1]

(b) Describe what happens to the particles of the spring during compression. [3]

(c) Define elastic limit. [2]

(d) Describe what would happen if the compression force exceeds the elastic limit. [2]

Answer 

(a) Compression.

(b) The particles are pushed closer together. The distances between particles decrease. The spring becomes shorter in length.

(c) The elastic limit is the maximum force or deformation an object can experience and still return to its original shape when the force is removed.

(d) The spring would not return to its original length. Permanent deformation would occur.

Question 3

A ruler is placed across two supports and pressed down in the middle.

(a) Name the type of deformation occurring. [1]

(b) State which part of the ruler is under tension. [1]

(c) State which part is under compression. [1]

(d) Explain why bending involves both tension and compression. [3]

Answer 

(a) Bending.

(b) The lower surface is under tension.

(c) The upper surface is under compression.

(d) When bent, one side of the ruler stretches while the opposite side compresses. The stretching produces tension and the compression shortens the material on the other side.

Question 4

A student twists a metal wire.

(a) Name the type of force applied. [1]

(b) Define torsion. [2]

(c) Explain what determines whether the wire returns to its original shape. [3]

Answer 

(a) Torsion.

(b) Torsion is a twisting force where one end of an object is turned relative to the other end.

(c) If the applied force is within the elastic limit, the wire returns to its original shape. If the force exceeds the elastic limit, plastic deformation occurs and the wire remains twisted.

Question 5

A long thin wire and a short thick wire are made of the same material. The same force is applied to both.

(a) State which wire will stretch more. [1]

(b) Explain your answer. [3]

(c) State two factors that affect deformation. [2]

Answer 

(a) The long thin wire will stretch more.

(b) A longer wire stretches more because there is more material over which the force acts. A thinner wire has a smaller cross-sectional area, so the force causes a greater effect.

(c)

• Magnitude of the force
• Material of the object

Question 6

Explain the difference between elastic deformation and plastic deformation. [6]

Answer 

Elastic deformation occurs when an object changes size or shape under a force but returns to its original shape when the force is removed. This happens when the force is below the elastic limit.

Plastic deformation occurs when the object does not return to its original shape after the force is removed. This happens when the force exceeds the elastic limit and permanent changes occur in the arrangement of particles.

Question 7

A bridge is designed to bend slightly under heavy traffic.

(a) Explain why slight bending is desirable. [3]

(b) State what would happen if the elastic limit is exceeded. [2]

(c) Explain why engineers design structures below the elastic limit. [3]

Answer 

(a) Slight bending allows the bridge to absorb forces safely. It prevents cracking and reduces stress concentration.

(b) Permanent deformation or structural failure may occur.

(c) Operating below the elastic limit ensures that any deformation is temporary and the structure returns to its original shape, maintaining safety and stability.

Question 8

Car tyres deform where they touch the road.

(a) State why the tyre deforms. [2]

(b) Explain how this deformation improves grip. [3]

(c) State whether this deformation is elastic or plastic. [1]

Answer 

(a) The weight of the car applies a downward force on the tyres.

(b) Deformation increases the contact area between the tyre and the road. A larger contact area increases friction and improves grip.

(c) Elastic deformation.

Question 9

A paperclip is bent and remains bent.

(a) State the type of deformation. [1]

(b) Explain what has happened at the particle level. [3]

(c) Define elastic limit in relation to this example. [2]

Answer 

(a) Plastic deformation.

(b) The applied force exceeded the elastic limit. The particles moved permanently into new positions. The bonds between particles were rearranged.

(c) The elastic limit is the maximum force the paperclip could withstand and still return to its original shape.

Question 10

A spring stretches 2 cm under a small load and 6 cm under a larger load.

(a) State the relationship between force and deformation within the elastic limit. [2]

(b) What may happen if the load continues to increase? [2]

(c) Name the law that describes the relationship between force and extension. [1]

Answer 

(a) Within the elastic limit, extension increases proportionally with applied force.

(b) The spring may exceed its elastic limit and become permanently stretched.

(c) Hooke’s law.

Question 11

Describe three practical applications where elastic deformation is useful. [6]

Answer 

• Car suspension systems absorb shocks from uneven roads.
• Shock absorbers reduce impact forces.
• Mattresses and cushions provide comfort by distributing weight evenly.

In each case, the material returns to its original shape after the force is removed.

Question 12

Glass often breaks instead of deforming plastically.

(a) Explain why glass behaves differently from rubber. [3]

(b) State whether glass has a high or low elastic limit. [1]

(c) Explain why this property makes glass brittle. [2]

Answer 

(a) Glass has strong but rigid bonds between particles. It cannot rearrange easily under stress. Rubber has flexible molecular chains that allow stretching.

(b) Glass has a low elastic limit.

(c) Because it cannot deform plastically, it breaks suddenly when the elastic limit is exceeded.

Question 13

A student performs an experiment to investigate how a spring stretches when different loads are applied.

(a) Define the term load. [2]

(b) State the formula used to calculate load. [1]

(c) Define extension. [2]

(d) A spring has an original length of 0.20 m. When a load is applied, its length becomes 0.26 m.

Calculate the extension. [2]

Answer

(a) Load is the force applied to an object, usually produced by hanging masses.

(b) Load = mass × gravitational field strength

(c) Extension is the increase in length of an object caused by an applied force.

(d)

Extension = stretched length − original length

Extension = 0.26 − 0.20

Extension = 0.06 m

Question 14

The graph below shows the load–extension relationship for a metal spring.

(a) State the region where Hooke’s law is obeyed. [1]

(b) State Hooke’s law. [2]

(c) Describe the shape of the graph beyond the limit of proportionality. [2]

(d) Explain why the graph no longer remains a straight line beyond this point. [3]

Answer 

(a) The straight-line region through the origin.

(b) Hooke’s law states that load is directly proportional to extension provided the elastic limit is not exceeded.

(c) The graph curves and is no longer linear.

(d) Beyond the limit of proportionality, extension increases more rapidly for each additional load. The material no longer obeys a proportional relationship between load and extension.

Question 15

Describe how you would carry out a load–extension experiment using a spring. [8]

Answer 

• Set up a clamp stand with the spring hanging vertically.
• Attach a pointer to the lower end of the spring.
• Place a ruler next to the spring to measure length.
• Measure and record the original length without load.
• Add a small known mass to provide a load.
• Measure the new length and calculate extension.
• Increase the load in equal steps and repeat measurements.
• Record results in a table and avoid exceeding the elastic limit.

Question 16

A student plots a load–extension graph.

(a) State which quantity is placed on the horizontal axis. [1]

(b) State which quantity is placed on the vertical axis. [1]

(c) Explain how the gradient of the graph is related to stiffness. [3]

(d) Explain what a steeper gradient indicates. [2]

Answer 

(a) Extension.

(b) Load.

(c) The gradient of the straight-line section equals load divided by extension. This represents stiffness.

(d) A steeper gradient indicates a stiffer object that requires a larger load to produce a given extension.

Question 17

A wire is loaded beyond its elastic limit and then unloaded.

(a) Define elastic limit. [2]

(b) Describe what happens when the wire is unloaded. [3]

(c) Define permanent extension. [2]

Answer 

(a) The elastic limit is the maximum load that allows an object to return to its original length when the load is removed.

(b) The unloading curve does not follow the original path. The wire does not return to its original length.

(c) Permanent extension is the remaining increase in length after the load has been removed.

Question 18

Explain the difference between the limit of proportionality and the elastic limit. [6]

Answer 

• The limit of proportionality is the point where the straight-line section of the graph ends and extension is no longer directly proportional to load.
• The elastic limit is the maximum load that allows the material to return to its original length.
• The limit of proportionality occurs before the elastic limit. Between these two points, the material may still return to its original length but no longer obeys Hooke’s law.

Question 19

A spring extends 0.04 m when a load of 8 N is applied. It extends 0.08 m when a load of 16 N is applied.

(a) State whether the spring obeys Hooke’s law. Explain. [3]

(b) Calculate the stiffness of the spring. [3]

Answer 

(a) Yes. The extension doubles when the load doubles. This shows load is directly proportional to extension.

(b)

Stiffness = Load / Extension

Stiffness = 8 / 0.04

Stiffness = 200 N m⁻¹

Question 20

Describe the appearance of a correct sketch of a load–extension graph in an exam. [6]

Answer

• Axes labeled correctly with load and extension.
• Straight line through the origin in the elastic region.
• Curved section beyond the limit of proportionality.
• Clear indication of the elastic limit if required.
• Appropriate shape and smooth curve.
• Graph should reflect proportional and non-proportional regions clearly.

Question 21

A thick steel wire and a thin steel wire of equal length are tested.

(a) State which wire has a steeper load–extension graph. [1]

(b) Explain your answer. [3]

(c) State one practical reason why thick wires are used in construction. [2]

Answer 

(a) The thick wire.

(b) A thicker wire has a larger cross-sectional area and greater stiffness. It requires a larger load to produce the same extension.

(c) Thick wires can support larger loads without excessive extension.

Question 22

State four precautions that should be taken during a load–extension experiment. [4]

Answer 

• Read the ruler at eye level to avoid parallax error.
• Use a pointer to improve accuracy.
• Add loads gradually.
• Do not exceed the elastic limit.

Question 23

Explain why safety goggles are worn during a load–extension experiment. [2]

Answer 

If the spring or wire snaps under tension, it may recoil suddenly and cause injury. Safety goggles protect the eyes.

Question 24

Explain why load–extension graphs are important in engineering. [6]

Answer 

• Load–extension graphs show how materials respond to forces.
• Engineers use them to determine stiffness, elastic limits, and safe working loads.
• They help ensure materials are used within their elastic range to prevent permanent damage or structural failure.

Question 25

A student obtains a curved graph from the start instead of a straight line.

(a) State one possible reason. [2]

(b) Explain how this affects calculations of stiffness. [3]

Answer 

(a) The elastic limit may have already been exceeded, or measurements may be inaccurate.

(b) Stiffness can only be calculated from the straight-line region. If the graph is curved from the start, proportionality does not exist and stiffness cannot be determined accurately.

Question 26

Three horizontal forces act on an object:

15 N to the right, 25 N to the right, and 30 N to the left.

(a) Calculate the total force acting to the right. [2]

(b) Calculate the resultant force on the object. [3]

(c) State the direction of the resultant force. [1]

(d) State what effect this resultant force will have on the motion of the object. [2]

Answer

(a) Total rightward force = 15 + 25 = 40 N

(b) Resultant force = 40 − 30 = 10 N

(c) To the right

(d) The object will accelerate to the right since there is a non-zero resultant force.

Question 27

Define the term resultant force. [2]

An object experiences two forces of equal magnitude acting in opposite directions.

(a) Calculate the resultant force. [2]

(b) Describe the motion of the object if it was initially at rest. [2]

(c) Describe the motion if it was already moving at constant speed. [2]

Answer 

Resultant force is the single force that has the same effect as all the forces acting together.

(a) Resultant force = 0 N

(b) If initially at rest, it remains at rest.

(c) If already moving, it continues moving at constant speed in a straight line.

Question 28

A box is pulled to the right with a force of 50 N. Friction acts to the left with a force of 35 N.

(a) Calculate the resultant force. [3]

(b) State whether the forces are balanced or unbalanced. [1]

(c) Explain the effect on the motion of the box. [3]

Answer 

(a) Resultant force = 50 − 35 = 15 N

(b) Unbalanced

(c) Since there is a resultant force of 15 N to the right, the box will accelerate to the right.

Question 29

Explain what is meant by equilibrium. [3]

State two situations in which an object can be in equilibrium. [2]

Answer 

Equilibrium occurs when the resultant force acting on an object is zero.

An object can be in equilibrium when:

• It is stationary
• It is moving at constant speed in a straight line

Question 30

An elevator has a weight of 5000 N. The tension in the supporting cable is also 5000 N.

(a) Calculate the resultant force. [2]

(b) State whether the elevator is in equilibrium. [1]

(c) Describe two possible motions of the elevator. [3]

Answer 

(a) Resultant force = 5000 − 5000 = 0 N

(b) Yes

(c) It may be stationary or moving upward or downward at constant speed.

Question 31

Describe how a free-body diagram is drawn for an object experiencing forces along a straight line. [6]

Answer 

• Represent the object as a simple shape such as a box or dot.
• Draw arrows to represent each force.
• The length of each arrow shows magnitude.
• The direction of the arrow shows direction of force.
• Label each force clearly.
• Ensure all forces acting on the object are included.

Question 32

Three forces act along a straight horizontal line:

40 N to the left, 10 N to the right, and 15 N to the right.

(a) Calculate the total rightward force. [2]

(b) Calculate the resultant force. [3]

(c) State the direction of the resultant force. [1]

(d) State whether the object is in equilibrium. [1]

Answer 

(a) Total rightward force = 10 + 15 = 25 N

(b) Resultant force = 40 − 25 = 15 N

(c) To the left

(d) No

Question 33

A student forgets to include friction when calculating the resultant force on a moving object.

(a) Explain why this is incorrect. [3]

(b) State one common mistake students make when adding forces. [2]

Answer 

(a) Friction acts in the opposite direction to motion and affects the resultant force. Ignoring friction gives an incorrect value for the resultant.

(b) Adding forces without considering their directions.

Question 34

Two spring balances pull an object in opposite directions. One reads 20 N and the other reads 25 N.

(a) Calculate the resultant force. [3]

(b) State the direction of motion. [2]

(c) Explain how this can be demonstrated experimentally. [3]

Answer 

(a) Resultant force = 25 − 20 = 5 N

(b) In the direction of the 25 N force

(c) Attach two spring balances to opposite sides of an object. Pull simultaneously and observe that the object moves in the direction of the larger force.

Question 35

Explain why zero resultant force does not necessarily mean that no forces are acting. [4]

Answer 

Zero resultant force means that the forces are balanced. Equal forces may be acting in opposite directions. These forces cancel each other out, producing no net force.

Question 36

A shopping trolley is pushed forward with a force of 60 N. Air resistance and friction together produce a backward force of 60 N.

(a) Calculate the resultant force. [2]

(b) State the motion of the trolley. [2]

(c) Explain your answer using the concept of equilibrium. [3]

Answer 36

(a) Resultant force = 0 N

(b) It moves at constant speed or remains stationary.

(c) The forces are balanced. When resultant force is zero, the object is in equilibrium and does not accelerate.

Question 37

A 1000 N force pulls a vehicle forward while resistive forces total 1200 N.

(a) Calculate the resultant force. [3]

(b) State the direction of acceleration. [2]

(c) Describe what happens to the vehicle’s speed. [2]

Answer 

(a) Resultant force = 1200 − 1000 = 200 N

(b) Backward

(c) The vehicle slows down.

Question 38

Explain how forces acting along the same straight line combine. [4]

Answer 

Forces acting in the same direction are added together. Forces acting in opposite directions are subtracted. The larger total determines the direction of the resultant force.

Question 39

Describe a simple experiment to investigate the effect of collinear forces on motion. [6]

Answer 

• Place an object on a smooth horizontal surface.
• Attach a spring balance to pull it forward.
• Measure the pulling force.
• Measure friction using another spring balance pulling backward.
• Calculate the resultant force.
• Observe the motion and relate it to the resultant force.

Question 40

A book rests on a table.

(a) Name the two main vertical forces acting on the book. [2]

(b) State their directions. [2]

(c) Explain why the book remains at rest. [3]

Answer 

(a) Weight and normal reaction force

(b) Weight acts downward.

Normal reaction acts upward.

(c) The upward force equals the downward force. The resultant force is zero, so the book is in equilibrium.

Question 41

(a) State Newton’s First Law of Motion. [3]

(b) Explain what is meant by a resultant force. [2]

(c) State two effects a resultant force can have on an object. [2]

Answer 

(a) An object remains at rest or continues to move at constant speed in a straight line unless acted on by a resultant force.

(b) A resultant force is the single force that has the same effect as all the forces acting together.

(c) A resultant force can cause an object to change speed or change direction.

Question 42

A book is resting on a table.

(a) Name the two forces acting on the book. [2]

(b) State why the book remains at rest. [2]

(c) Define equilibrium. [2]

Answer

(a) Weight and normal reaction force.

(b) The forces are equal in magnitude and opposite in direction, so the resultant force is zero.

(c) Equilibrium is the state in which the resultant force acting on an object is zero.

Question 43

A car is moving at constant speed in a straight line.

(a) State the resultant force acting on the car. [1]

(b) Explain why the car does not accelerate. [3]

(c) Identify two forces that may be acting on the car. [2]

Answer 

(a) Zero.

(b) The driving force is balanced by friction and air resistance. Since the forces are balanced, the resultant force is zero and there is no acceleration.

(c) Driving force and air resistance.

Question 44

Define inertia. [2]

(a) State how mass affects inertia. [2]

(b) Give one example of inertia in everyday life. [2]

Answer 

Inertia is the tendency of an object to resist changes in its state of motion.

(a) An object with greater mass has greater inertia and is harder to start or stop.

(b) Passengers moving forward when a bus suddenly stops.

Question 45

Explain why passengers in a car move forward when the car stops suddenly. [4]

Answer 

When the car stops suddenly, the car experiences a force that reduces its speed. However, passengers continue moving forward due to inertia. Their bodies tend to maintain their state of motion until a force, such as a seatbelt, acts on them.

Question 46

A spacecraft in deep space moves with engines switched off.

(a) Describe its motion. [2]

(b) Explain your answer using Newton’s First Law. [3]

Answer 

(a) It continues moving at constant speed in a straight line.

(b) In deep space, there is almost no friction or air resistance, so there is no resultant force acting on the spacecraft. According to Newton’s First Law, it continues in uniform motion.

Question 47

A ball rolls along the ground and gradually stops.

(a) State the force responsible for slowing the ball. [1]

(b) Explain how this force affects the motion. [3]

(c) State what would happen if there were no friction. [2]

Answer 

(a) Friction.

(b) Friction acts opposite to the direction of motion, creating an unbalanced force that slows the ball until it stops.

(c) The ball would continue moving at constant speed.

Question 48

Explain the difference between balanced and unbalanced forces. [4]

Answer 48

• Balanced forces are equal in magnitude and opposite in direction, producing zero resultant force and no change in motion.
• Unbalanced forces produce a non-zero resultant force, causing acceleration or change in motion.

Question 49

A trolley is stationary. A force of 20 N is applied forward, and friction is 20 N backward.

(a) Calculate the resultant force. [2]

(b) Describe the motion of the trolley. [2]

(c) Explain your answer. [3]

Answer

(a) Resultant force = 20 − 20 = 0 N

(b) The trolley remains at rest.

(c) The forces are balanced, so there is no resultant force to change its state of rest.

Question 50

Describe an experiment that demonstrates Newton’s First Law. [6]

Answer 50

•  Use an air track to reduce friction.
• Place a glider on the track.
• Push the glider gently.
• Observe that it moves at nearly constant speed.
• This shows that without significant friction, motion continues without a force.
• Conclude that force is needed to change motion, not maintain it.

Question 51

A heavy truck and a light car are initially at rest.

(a) Which requires a larger force to start moving? [1]

(b) Explain your answer using inertia. [3]

Answer 

(a) The heavy truck.

(b) The truck has greater mass and therefore greater inertia. It resists changes in motion more strongly, so a larger force is needed to start it moving.

Question 52

Explain why a force is required to change direction of motion. [4]

Answer 

Changing direction means changing velocity. Since velocity includes direction, any change requires acceleration. Acceleration occurs only when there is a resultant force.

Question 53

Define static equilibrium and dynamic equilibrium. [4]

Answer 

• Static equilibrium occurs when an object is at rest and the resultant force is zero.
• Dynamic equilibrium occurs when an object moves at constant speed in a straight line and the resultant force is zero.

Question 54

A cyclist stops pedalling and continues moving forward for a short distance before stopping.

(a) Explain why the cyclist continues moving after pedalling stops. [3]

(b) Explain why the cyclist eventually stops. [3]

Answer 

(a) Due to inertia, the cyclist continues moving because no immediate resultant force acts to stop the motion.

(b) Friction and air resistance act opposite to the direction of motion, creating an unbalanced force that slows and stops the cyclist.

Question 55

A student says, “A force is needed to keep an object moving at constant speed.”

(a) State whether this statement is correct. [1]

(b) Explain your answer. [4]

Answer 55

(a) Incorrect.

(b) A force is only required to change motion. If an object moves at constant speed in a straight line, the resultant force is zero. Forces such as friction require a continuous force to balance them, but motion itself does not require a force.

Question 56

Explain how seatbelts reduce injury in a car accident. [5]

Answer 

When a car stops suddenly, passengers continue moving forward due to inertia. The seatbelt provides a force that slows the passenger safely. It increases the time over which the stopping force acts, reducing the risk of injury.

Question 57

Describe two real-life applications of Newton’s First Law in engineering. [4]

Answer 

• Design of seatbelts and airbags in vehicles.
• Design of crumple zones to absorb impact forces.

Question 58

A hockey puck slides across smooth ice.

(a) Describe its motion. [2]

(b) Explain why it eventually slows down. [3]

Answer 

(a) It moves at nearly constant speed in a straight line.

(b) Small frictional forces and air resistance act on it, creating a small resultant force that gradually slows it down.

Question 59

A car travels around a circular bend at constant speed.

(a) State whether the car is accelerating. [1]

(b) Explain your answer. [3]

(c) Identify the force responsible for this motion. [2]

Answer 

(a) Yes.

(b) Although the speed remains constant, the direction of motion changes. Since velocity includes direction, the velocity is changing. A change in velocity means acceleration.

(c) Friction between the tyres and the road provides the force towards the centre of the circle.

Question 60

A stone is tied to a string and swung in a horizontal circle.

(a) State the direction of the velocity at any point. [2]

(b) State the direction of the resultant force. [2]

(c) Explain how this force affects the motion. [3]

Answer 

(a) The velocity is tangent to the circular path.

(b) Towards the centre of the circle.

(c) The force continuously changes the direction of the velocity, keeping the stone moving in a circular path.

Question 61

Explain why a change in direction alone is sufficient to produce acceleration. [4]

Answer 

Acceleration is defined as the rate of change of velocity. Velocity includes both speed and direction. Even if speed remains constant, a change in direction means velocity changes. Therefore, acceleration occurs.

Question 62

A ball is thrown vertically upward.

(a) State the force acting on the ball during its motion. [1]

(b) Explain how this force affects the ball as it rises. [3]

(c) Explain how this force affects the ball as it falls. [3]

Answer 

(a) Gravitational force.

(b) The force acts downward, opposite to the motion, causing the ball to slow down as it rises.

(c) The force acts in the same direction as the motion when falling, causing the ball to speed up.

Question 63

A car is skidding while turning a corner.

(a) Explain how the resultant force changes the direction of motion. [3]

(b) Explain how it may also change the speed. [3]

Answer 

(a) A sideways force towards the centre of the turn changes the direction of velocity.

(b) If braking or friction reduces forward motion, the speed also decreases. Thus the resultant force can change both speed and direction.

Question 64

State the effect of a force acting:

(a) In the same direction as motion. [2]

(b) Opposite to motion. [2]

(c) At right angles to motion. [2]

(d) At an angle to motion. [2]

Answer 

(a) Increases speed.

(b) Decreases speed.

(c) Changes direction without changing speed.

(d) Changes both speed and direction.

Question 65

A cyclist turns a corner at constant speed.

(a) Is the resultant force zero? [1]

(b) Explain your answer. [3]

(c) Identify the force that enables turning. [2]

Answer 

(a) No.

(b) The direction of velocity changes, so there must be a resultant force acting towards the centre of the turn.

(c) Friction between the tyres and the road.

Question 66

Explain the relationship between resultant force and acceleration. [4]

Answer 

A resultant force causes acceleration. Acceleration is the rate of change of velocity. If the resultant force is zero, there is no acceleration. If the resultant force is non-zero, the object accelerates.

Question 67

Describe how a velocity–time graph shows constant velocity. [3]

Answer

A horizontal straight line represents constant velocity. The slope of the graph is zero, indicating no acceleration and zero resultant force.

Question 68

A sloping straight line on a velocity–time graph represents acceleration.

(a) What does the slope represent? [2]

(b) What does this indicate about the resultant force? [2]

Answer 

(a) The slope represents acceleration.

(b) A non-zero slope indicates a non-zero resultant force.

Question 69

A football is kicked along the ground and gradually slows down.

(a) Identify the force responsible. [1]

(b) Explain how this force affects velocity. [3]

(c) State what would happen if there were no friction. [2]

Answer 

(a) Friction.

(b) Friction acts opposite to motion, reducing the speed and therefore changing velocity.

(c) The football would continue moving at constant speed.

Question 70

An elevator begins to move upward from rest.

(a) Describe the forces acting. [3]

(b) Explain why the elevator accelerates upward. [3]

Answer 

(a) Tension acts upward and weight acts downward.

(b) The tension is greater than the weight, producing an upward resultant force and acceleration.

Question 71

Explain why balanced forces result in constant velocity. [4]

Answer 

Balanced forces produce zero resultant force. Without a resultant force, there is no acceleration. Since acceleration is zero, velocity remains constant.

Question 72

A trolley moves along a curved track at nearly constant speed.

(a) Explain why there is acceleration. [3]

(b) State the direction of the resultant force. [2]

Answer 

(a) The direction of motion changes, so velocity changes. A change in velocity means acceleration.

(b) Towards the centre of the curve.

Question 73

Describe one experiment that demonstrates how a force changes direction without changing speed. [6]

Answer 

• Use a trolley on a curved track.
• Push it gently so it moves at nearly constant speed.
• Observe that it follows the curve.
• The track provides a sideways force.
• The speed remains nearly constant.
• Conclude that a sideways force changes direction but not speed.

Question 74

A student says, “If speed does not change, there is no acceleration.”

(a) State whether this is correct. [1]

(b) Explain your answer. [4]

Answer 

(a) Incorrect.

(b) Acceleration is change in velocity. Velocity includes direction. Even if speed stays the same, a change in direction means acceleration occurs.

Question 75

Explain why a car requires friction to turn safely. [4]

Answer 

Friction provides the sideways force towards the centre of the turn. Without sufficient friction, there would be no centripetal force and the car would move in a straight line instead of turning.

Question 76

State two examples where a resultant force changes both speed and direction simultaneously. [4]

Answer 

• A ball thrown at an angle under gravity.
• A car skidding while turning.

In both cases, the force changes speed and direction.

Question 77

(a) Define solid friction. [3]

(b) State the direction in which solid friction acts. [2]

(c) Explain why friction is necessary for walking. [3]

Answer 

(a) Solid friction is the force that acts between two solid surfaces in contact and opposes their relative motion or tendency to move.

(b) It acts parallel to the surfaces and opposite to the direction of motion or attempted motion.

(c) When walking, the foot pushes backward on the ground. Static friction between the shoe and the ground prevents slipping and provides a forward force that allows movement.

Question 78

Explain how microscopic irregularities cause solid friction. [4]

Answer 78

Even surfaces that appear smooth have tiny bumps and valleys called asperities. When two surfaces are pressed together, these irregularities interlock. This interlocking resists motion and produces friction.

Question 79

State two main causes of solid friction. [2]

Explain each briefly. [4]

Answer

• Microscopic roughness of surfaces, which causes interlocking.
• Molecular attraction between surfaces at contact points.

Both factors resist motion between the surfaces.

Question 80

Distinguish between static friction and kinetic friction. [4]

Answer

• Static friction acts when surfaces are in contact but not moving relative to each other. It prevents motion from starting.
• Kinetic friction acts when surfaces are sliding over each other and opposes motion.

Question 81

A student pushes a heavy box, but it does not move.

(a) Identify the type of friction acting. [1]

(b) Explain why the box does not move. [3]

(c) State what must happen for the box to start moving. [2]

Answer 

(a) Static friction.

(b) Static friction balances the applied force. The resultant force is zero, so there is no motion.

(c) The applied force must exceed the maximum static friction.

Question 82

A book slides across a table and slows down.

(a) Identify the type of friction acting. [1]

(b) Explain why the book slows down. [3]

(c) State what would happen if friction were absent. [2]

Answer 

(a) Kinetic friction.

(b) Friction acts opposite to motion, creating a resultant force that reduces speed.

(c) The book would continue moving at constant speed.

Question 83

Explain how friction produces heating. [4]

Answer 

When surfaces slide over each other, work is done against friction. This work converts mechanical energy into thermal energy. As a result, the temperature of the surfaces increases.

Question 84

Describe the energy changes when a car brakes. [5]

Answer 

The car’s kinetic energy decreases. Friction between the brake pads and discs converts kinetic energy into thermal energy. The brakes become hot as a result.

Question 85

State two factors that affect the magnitude of friction. [2]

Explain how each factor affects friction. [4]

Answer 

• Nature of the surfaces. Rough surfaces produce more friction than smooth surfaces.
• Force pressing surfaces together. Greater force increases friction.

Question 86

Explain why a heavier box is harder to push across the same floor than a lighter box. [4]

Answer 

A heavier box exerts a greater force on the floor. This increases the normal contact force between surfaces, resulting in greater friction. Therefore, more force is needed to move it.

Question 87

State three advantages of solid friction. [3]

Answer 

• Enables walking.
• Allows vehicles to accelerate and brake.
• Helps grip objects securely.

Question 88

State three disadvantages of solid friction. [3]

Answer 

• Causes wear and tear.
• Produces unwanted heat.
• Reduces efficiency of machines.

Question 89

Describe two methods of reducing friction. [4]

Answer 

• Lubrication using oil or grease to reduce direct contact.

• Using ball bearings to replace sliding friction with rolling friction.

Question 90

Explain why ball bearings reduce friction. [4]

Answer 

Ball bearings replace sliding friction with rolling friction. Rolling friction is much smaller because there is less surface contact and less interlocking of asperities.

Question 91

Explain why tyre treads are designed to increase friction. [4]

Answer 

Tyre treads increase grip by improving contact with the road surface. This increases friction, allowing safer acceleration, braking, and turning.

Question 92

Describe an experiment to measure friction using a spring balance. [6]

Answer 

• Place a wooden block on a horizontal surface.
• Attach a spring balance to the block.
• Pull gently and record the force just as motion begins.
• This gives maximum static friction.
• Continue pulling at constant speed and record the force.
• This gives kinetic friction.

Question 93

A student repeats a friction experiment using different surfaces.

(a) Predict how results will change for a rough surface. [2]

(b) Explain your answer. [3]

Answer 

(a) The frictional force will increase.

(b) Rough surfaces have more irregularities that interlock, increasing resistance to motion.

Question 94

Explain why friction is essential for driving a car. [5]

Answer 

Friction between tyres and the road allows forward motion when accelerating. It allows braking by opposing motion. It provides the sideways force needed for turning. Without friction, control of the vehicle would not be possible.

Question 95

A machine becomes very hot during operation.

(a) Explain why friction causes this heating. [3]

(b) Suggest one way engineers reduce this problem. [2]

Answer 

(a) Friction converts mechanical energy into thermal energy, increasing temperature.

(b) Use lubrication to reduce friction.

Question 96

A student states that friction only acts when objects are moving.

(a) Is this statement correct? [1]

(b) Explain your answer. [3]

Answer 

(a) No.

(b) Static friction acts even when objects are not moving. It prevents motion from starting.

Question 97

Explain why smoother surfaces do not have zero friction. [4]

Answer 

Even smooth surfaces have microscopic irregularities and molecular attraction at contact points. These effects produce friction.

Question 98

Describe how friction affects energy efficiency in machines. [4]

Answer 

Friction converts useful mechanical energy into unwanted thermal energy. This reduces the efficiency of machines because less energy is available for useful work.

Question 99

Explain why it is easier to keep a box moving than to start moving it. [4]

Answer 

Maximum static friction is usually greater than kinetic friction. Therefore, a larger force is required to overcome static friction initially than to maintain motion once sliding begins.

Question 100

Discuss both the advantages and disadvantages of solid friction in everyday life. [6]

Answer 

Advantages include enabling walking, driving, gripping, and writing. Friction allows safe control of motion.

Disadvantages include wear and tear, production of unwanted heat, and reduction of machine efficiency. Engineers must balance the need for friction with methods to reduce it where necessary.

Question 101

(a) Define drag in liquids. [3]

(b) State the direction of drag relative to motion. [2]

(c) Explain why drag does not act on a stationary object in a liquid. [2]

Answer 

(a) Drag is the frictional force that acts on an object moving through a liquid and opposes its motion.

(b) It acts opposite to the direction of motion.

(c) Drag only occurs when there is relative motion between the object and the liquid. If the object is stationary relative to the liquid, no drag acts.

Question 102

Explain how viscous resistance contributes to drag in liquids. [4]

Answer

Liquids have viscosity, meaning they resist flow. As an object moves through a liquid, layers of liquid slide past each other. Internal friction between these layers resists motion and produces a drag force.

Question 103

Describe how pressure differences around a moving object contribute to drag. [4]

Answer 

As an object moves through a liquid, liquid in front of it is compressed, creating high pressure. Behind the object, pressure is lower. This pressure difference produces a backward force that contributes to drag.

Question 104

A swimmer moves forward through water.

(a) Identify the force opposing motion. [1]

(b) Explain why the swimmer must apply a continuous force. [3]

(c) State what would happen if the swimmer stopped applying force. [2]

Answer 104

(a) Drag.

(b) Drag acts opposite to motion. To maintain speed, the swimmer must apply a force equal to the drag force.

(c) The swimmer would slow down and eventually stop.

Question 105

Explain how drag changes with increasing speed. [4]

Answer 

At low speeds, drag increases approximately proportionally with speed. At higher speeds, drag increases much more rapidly. Therefore, a small increase in speed requires a much larger force to overcome drag.

Question 106

Describe how streamlining reduces drag. [4]

Answer 

Streamlined shapes allow liquid to flow smoothly around the object. This reduces turbulence and pressure differences, lowering the drag force.

Question 107

State how surface area affects drag. [2]

Explain why this occurs. [3]

Answer 

• Larger surface area increases drag.
• More liquid must be displaced, and more contact occurs between the object and liquid, increasing resistive forces.

Question 108

Explain how viscosity affects drag. [4]

Answer 

Liquids with higher viscosity have greater internal friction between layers. This increases resistance to motion and results in greater drag on objects moving through them.

Question 109

A metal ball is dropped into water.

(a) Name the three forces acting on it. [3]

(b) State the direction of each force. [3]

Answer 

(a) Weight, upthrust, drag.

(b) Weight acts downward. Upthrust acts upward. Drag acts upward while the ball is falling.

Question 110

Explain how terminal velocity is reached when an object falls through a liquid. [6]

Answer 

Initially, weight is greater than drag and upthrust, so the object accelerates downward. As speed increases, drag increases. Eventually, drag plus upthrust equals weight. The resultant force becomes zero, so acceleration stops and the object continues falling at constant speed called terminal velocity.

Question 111

Define terminal velocity. [2]

State the condition of forces at terminal velocity. [2]

Answer 

Terminal velocity is the constant maximum speed reached by an object falling through a liquid.

At terminal velocity, weight equals drag plus upthrust.

Question 112

Explain why terminal velocity in liquids is usually lower than in air. [4]

Answer 

Liquids are denser and more viscous than air. They produce much greater drag forces. As a result, forces balance at lower speeds, giving a lower terminal velocity.

Question 113

A toy boat is pushed across water and then released.

(a) Explain why it slows down. [3]

(b) State what would happen in the absence of drag. [2]

Answer 

(a) Drag acts opposite to motion, creating a resultant force that reduces speed.

(b) It would continue moving at constant speed.

Question 114

Explain how upthrust and drag act together on a rising bubble in water. [5]

Answer 

Upthrust acts upward and is greater than weight, causing the bubble to rise. As the bubble rises, drag acts downward opposite to motion. Eventually, drag plus weight equals upthrust, and the bubble rises at constant speed.

Question 115

Describe one experiment to investigate drag in liquids. [6]

Answer 

• Fill a tall cylinder with water or oil.
• Drop a small sphere into the liquid.
• Measure the time taken to fall a known distance.
• Repeat for different liquids or spheres.
• Observe changes in falling speed.
• Conclude how drag depends on viscosity and shape.

Question 116

Explain why submarines are designed with smooth, streamlined shapes. [4]

Answer 

Streamlined shapes reduce turbulence and pressure differences in water. This reduces drag, improving speed and fuel efficiency.

Question 117

State two ways to reduce drag in liquids. [2]

Explain each briefly. [4]

Answer 

• Streamlining reduces turbulence.
• Polishing surfaces reduces friction between object and liquid.

Question 118

Give two situations where increasing drag is useful. [2]

Explain why in each case. [4]

Answer 

• Sea anchors increase drag to stabilize boats.
• Parachute-like devices in water rescue slow descent.

In both cases, increased drag reduces speed or increases control.

Question 119

Explain why stirring honey requires more effort than stirring water. [4]

Answer Honey has higher viscosity than water. Greater internal friction produces larger drag forces. More force is required to overcome this resistance.

Question 120

A student says, “Drag only acts at high speeds.”

(a) State whether this is correct. [1]

(b) Explain your answer. [3]

Answer 

(a) Incorrect.

(b) Drag acts at all speeds when an object moves through a liquid. However, the magnitude of drag increases with speed.

Question 121

(a) Define air resistance. [3]

(b) State the direction in which air resistance acts. [2]

(c) State the condition required for air resistance to act on an object. [2]

Answer 

(a) Air resistance is the frictional force that acts on an object moving through air and opposes its motion.

(b) It acts opposite to the direction of motion.

(c) There must be relative motion between the object and the air.

Question 122

Explain why air resistance occurs when an object moves through air. [4]

Answer 

Air is made of molecules. When an object moves through air, it collides with air molecules and pushes them aside. These collisions and pressure differences around the object produce a backward force called air resistance.

Question 123

A cyclist rides forward on a road.

(a) Identify the force opposing motion through air. [1]

(b) Explain why this force increases with speed. [3]

(c) State one way the cyclist can reduce this force. [2]

Answer 

(a) Air resistance.

(b) At higher speeds, the cyclist collides with more air molecules per second and produces greater pressure differences, increasing air resistance.

(c) By adopting a crouched position to reduce surface area.

Question 124

Explain how streamlining reduces air resistance. [4]

Answer

Streamlined shapes allow air to flow smoothly around the object. This reduces turbulence and pressure differences, decreasing the drag force acting on the object.

Question 125

A sheet of paper and a crumpled ball of paper are dropped from the same height.

(a) State which falls faster. [1]

(b) Explain why. [3]

(c) State what would happen in a vacuum. [2]

Answer 

(a) The crumpled ball.

(b) The sheet has a larger surface area and experiences greater air resistance. The crumpled ball has less air resistance.

(c) Both would fall at the same rate.

Question 126

Explain how air resistance affects falling objects. [5]

Answer 

At the start of the fall, air resistance is small, so the object accelerates downward. As speed increases, air resistance increases. Eventually, air resistance equals weight, resulting in zero resultant force and constant speed.

Question 127

(a) Define terminal velocity. [2]

(b) State the forces acting at terminal velocity. [2]

Answer 

(a) Terminal velocity is the constant maximum speed reached by a falling object when forces are balanced.

(b) At terminal velocity, weight equals air resistance.

Question 128

Describe how the motion of a skydiver changes from the moment of jumping until landing. [6]

Answer 

Initially, the skydiver accelerates downward because weight is greater than air resistance. As speed increases, air resistance increases until it equals weight. The skydiver reaches terminal velocity. When the parachute opens, surface area increases greatly, increasing air resistance and reducing speed to a new lower terminal velocity.

Question 129

Explain why a stone falls faster than a feather in air. [4]

Answer 

The feather has a large surface area relative to its weight, producing large air resistance. The stone has greater weight and smaller surface area relative to mass, so air resistance affects it less.

Question 130

Explain why vehicles require more power at higher speeds. [4]

Answer 

Air resistance increases rapidly with speed. At high speeds, much of the engine’s power is used to overcome air resistance. Therefore, more power is needed to maintain higher speeds.

Question 131

State two advantages of air resistance. [2]

Explain each briefly. [4]

Answer 

• Slows falling objects, improving safety.
• Allows parachutes to reduce speed safely.

Air resistance balances weight and limits maximum speed.

Question 132

State two disadvantages of air resistance. [2]

Explain each briefly. [4]

Answer 

• Increases fuel consumption.
• Reduces maximum speed of vehicles.

Energy is transferred from the vehicle to the air, reducing efficiency.

Question 133

A racing car is redesigned to reduce air resistance.

(a) Suggest two design changes. [2]

(b) Explain why these changes reduce drag. [4]

Answer 

(a) Make the car more streamlined and reduce surface roughness.

(b) Streamlining reduces turbulence and pressure differences. Smooth surfaces reduce friction with air molecules.

Question 134

Explain why air resistance acts upward on a falling object. [3]

Answer 

Air resistance always acts opposite to motion. Since the object moves downward, air resistance acts upward.

Question 135

Describe an experiment that demonstrates the effect of air resistance. [6]

Answer 

• Drop a flat sheet of paper and a crumpled paper from the same height.
• Observe the difference in falling speed.
• Explain that the flat sheet experiences greater air resistance due to larger surface area.
• Conclude that air resistance affects motion.

Question 136

Explain the energy changes that occur when air resistance slows a moving object. [4]

Answer 

Kinetic energy of the object decreases. Work is done against air resistance. Energy is transferred to the air as thermal energy and kinetic energy of air molecules.

Question 137

A student states that air resistance only acts at high speeds.

(a) State whether this is correct. [1]

(b) Explain your answer. [3]

Answer 

(a) Incorrect.

(b) Air resistance acts at all speeds when there is motion relative to air. However, it increases significantly at higher speeds.

Question 138

Explain why aircraft must be carefully shaped to reduce air resistance. [4]

Answer 

Reducing air resistance improves fuel efficiency and speed. Streamlined shapes reduce turbulence and drag, allowing smoother airflow and better performance.

Question 139

Describe how a parachute increases air resistance. [4]

Answer 

A parachute increases surface area facing the airflow. This greatly increases air resistance, reducing the skydiver’s speed and lowering terminal velocity.

Question 140

Discuss the similarities and differences between solid friction and air resistance. [6]

Answer 

Similarities: Both oppose motion and convert mechanical energy into thermal energy.

Differences: Solid friction occurs between solid surfaces in contact. Air resistance occurs when an object moves through air. Air resistance depends strongly on speed and shape, while solid friction depends mainly on surface type and normal force.

Question 141

(a) Define the spring constant. [2]

(b) State the equation linking spring constant, force, and extension. [2]

(c) State the unit of spring constant. [1]

Answer

(a) The spring constant is the force per unit extension of a spring.

(b) k = F / x

(c) Newton per metre (N/m).

Question 142

A force of 12 N produces an extension of 0.03 m in a spring.

(a) Calculate the spring constant. [3]

(b) State whether the spring is relatively stiff or soft. [2]

Answer 

(a)

k = F / x

k = 12 / 0.03

k = 400 N/m

(b) The spring is relatively stiff because it requires a large force to produce a small extension.

Question 143

A spring has a spring constant of 250 N/m.

(a) Calculate the force required to produce an extension of 0.04 m. [3]

(b) State the formula used. [1]

Answer 

(a)

F = kx

F = 250 × 0.04

F = 10 N

(b) F = kx

Question 144

A spring has a spring constant of 500 N/m. A force of 20 N is applied.

(a) Calculate the extension produced. [3]

(b) Convert your answer into centimetres. [1]

Answer 

(a)

x = F / k

x = 20 / 500

x = 0.04 m

(b) 4 cm

Question 145

Explain the physical meaning of a large spring constant. [3]

Answer 

A large spring constant means the spring is stiff. A large force is needed to produce a small extension.

Question 146

Two springs, A and B, have spring constants of 600 N/m and 300 N/m respectively.

(a) State which spring is stiffer. [1]

(b) Explain your answer. [2]

(c) For the same force applied, compare their extensions. [2]

Answer 

(a) Spring A.

(b) It has the larger spring constant, meaning more force per unit extension.

(c) Spring A will extend half as much as Spring B for the same force.

Question 147

Describe how to determine the spring constant experimentally. [6]

Answer 

• Hang the spring from a clamp stand.
• Measure the original length.
• Add known masses gradually.
• Measure stretched length each time.
• Calculate extension for each force.
• Plot force against extension and find the gradient of the straight line.

Question 148

Explain how the spring constant can be found from a force–extension graph. [4]

Answer 

Force is plotted on the vertical axis and extension on the horizontal axis. The gradient of the straight-line section equals the spring constant.

Question 149

A student stretches a spring beyond its elastic limit.

(a) Explain why k = F / x no longer applies. [3]

(b) State what happens to the spring. [2]

Answer 

(a) Beyond the elastic limit, force is no longer proportional to extension. The spring constant is no longer constant.

(b) The spring undergoes permanent deformation.

Question 150

A spring extends 5 cm when a force of 15 N is applied.

(a) Convert the extension to metres. [1]

(b) Calculate the spring constant. [3]

Answer 

(a) 0.05 m

(b)

k = F / x

k = 15 / 0.05

k = 300 N/m

Question 151

Explain why extension must be measured in metres when using k = F / x. [3]

Answer 

The SI unit of force is newton and the SI unit of length is metre. To obtain the correct unit N/m for k, extension must be in metres.

Question 152

A spring has an original length of 0.15 m. It stretches to 0.21 m under a force of 18 N.

(a) Calculate the extension. [2]

(b) Calculate the spring constant. [3]

Answer 

(a)

Extension = 0.21 − 0.15 = 0.06 m

(b)

k = 18 / 0.06

k = 300 N/m

Question 153

Explain the relationship between Hooke’s law and the spring constant. [4]

Answer

Hooke’s law states that force is proportional to extension. The spring constant is the constant of proportionality between force and extension.

Question 154

A force–extension graph is a straight line through the origin.

(a) What does this indicate about the spring? [2]

(b) What does the gradient represent? [2]

Answer 

(a) The spring obeys Hooke’s law.

(b) The gradient represents the spring constant.

Question 155

Explain why car suspension systems use springs with large spring constants. [4]

Answer 

Car suspensions must support large loads without excessive extension. A large spring constant ensures small extensions under heavy forces, providing stability and safety.

Question 156

A spring constant is mistakenly calculated using total length instead of extension.

(a) Explain why this is incorrect. [3]

(b) Define extension correctly. [2]

Answer 

(a) The equation uses extension, not total length. Using total length gives an incorrect value for k.

(b) Extension is the increase in length from the original length.

Question 157

A spring stretches 0.02 m under a 4 N force and 0.04 m under an 8 N force.

(a) Does the spring obey Hooke’s law? [2]

(b) Explain your reasoning. [2]

Answer 

(a) Yes.

(b) When force doubles, extension doubles, showing proportionality.

Question 158

Explain why the spring constant remains constant only within the elastic limit. [4]

Answer 

Within the elastic limit, force and extension are proportional. Beyond this limit, permanent deformation occurs and proportionality no longer holds, so k is not constant.

Question 159

State two real-life devices that rely on a known spring constant. [2]

Explain briefly. [4]

Answer

• Spring balance, which measures weight using extension.
• Car suspension system, which controls motion using spring stiffness.
• Both rely on predictable force–extension behavior.

Question 160

Discuss common misconceptions about the spring constant. [6]

Answer 

Some believe the spring constant changes as the spring stretches. It remains constant within the elastic limit. Others confuse extension with total length. Extension is the increase in length, not the full length. The equation must use extension in metres for accurate results.

Question 161

(a) Define the term limit of proportionality. [3]

(b) State what happens to the load–extension graph beyond this point. [2]

Answer 

(a) The limit of proportionality is the point on a load–extension graph beyond which extension is no longer directly proportional to load.

(b) The graph is no longer a straight line and begins to curve.

Question 162

Explain what is meant by two quantities being directly proportional. [3]

A spring obeys Hooke’s law up to a certain load.

(a) State how this is shown on a graph. [2]

Answer 

Two quantities are directly proportional if one doubles when the other doubles and their graph is a straight line through the origin.

(a) The graph is a straight line passing through the origin.

Question 163

A load–extension graph for a spring is plotted.

(a) State which quantity is plotted on the vertical axis. [1]

(b) State which quantity is plotted on the horizontal axis. [1]

(c) Explain how the limit of proportionality is identified on the graph. [3]

Answer 

(a) Load.

(b) Extension.

(c) It is the point where the straight-line section ends and the graph begins to curve.

Question 164

Describe the behavior of a spring below the limit of proportionality. [4]

Answer

Below the limit of proportionality, extension is directly proportional to load. The graph is a straight line through the origin. Hooke’s law applies and the gradient remains constant.

Question 165

Describe the behavior of a spring beyond the limit of proportionality. [4]

Answer

Beyond the limit of proportionality, extension is no longer directly proportional to load. The graph curves upwards and equal increases in load produce larger increases in extension.

Question 166

Explain why calculations using Hooke’s law must only be performed below the limit of proportionality. [4]

Answer 

Hooke’s law states that force is proportional to extension. This relationship only holds in the straight-line region of the graph. Beyond the limit of proportionality, the relationship is no longer proportional, so calculations using F = kx are no longer valid.

Question 167

A student states that the limit of proportionality is the point where the spring breaks.

(a) State whether this is correct. [1]

(b) Explain your answer. [3]

Answer 

(a) Incorrect.

(b) The limit of proportionality marks the end of the straight-line region of the graph. It does not necessarily mean the spring breaks.

Question 168

A load–extension graph shows a straight line from 0 N to 10 N. Beyond 10 N the graph curves.

(a) State the limit of proportionality. [2]

(b) Explain how you identified it. [2]

Answer 

(a) 10 N.

(b) It is the point where the straight line ends and the graph begins to curve.

Question 169

Explain why the limit of proportionality is important in experiments. [4]

Answer 

It defines the maximum load for which Hooke’s law applies. Staying below this limit ensures proportional behavior and accurate calculations. Exceeding it produces unreliable results.

Question 170

Describe how the limit of proportionality can be determined experimentally. [6]

Answer 

• Hang the spring vertically.
• Measure original length.
• Add masses gradually.
• Measure extension for each load.
• Plot load against extension.
• Identify where the straight-line pattern changes to a curve.

Question 171

Explain the difference between proportional and non-proportional regions on a load–extension graph. [4]

Answer

In the proportional region, load and extension increase at the same rate and the graph is straight. In the non-proportional region, extension increases more rapidly and the graph curves.

Question 172

A student calculates the spring constant using values taken beyond the limit of proportionality.

Explain why the answer is unreliable. [4]

Answer 

Beyond the limit of proportionality, force is not directly proportional to extension. The gradient is not constant, so the calculated spring constant is not valid.

Question 173

State two common mistakes students make regarding the limit of proportionality. [4]

Answer 

• Assuming it is the maximum load shown.
• Confusing it with the point where the spring breaks.

Question 174

Explain why the graph is a straight line in the proportional region. [4]

Answer 

Because force and extension are directly proportional. This constant ratio produces a straight-line relationship passing through the origin.

Question 175

A spring extends 2 cm under 5 N and 4 cm under 10 N.

(a) Does this data suggest the spring is below the limit of proportionality? [2]

(b) Explain your reasoning. [2]

Answer 

(a) Yes.

(b) When the load doubles, the extension doubles, showing proportionality.

Question 176

Explain how the gradient of the straight-line region relates to the spring constant. [4]

Answer 

The gradient equals force divided by extension. This ratio is the spring constant. A constant gradient indicates proportional behavior.

Question 177

Describe how you would label the limit of proportionality on a sketch graph in an examination. [4]

Answer 

Draw axes correctly. Show a straight line from the origin. Indicate where the graph begins to curve. Mark this point clearly and label it as the limit of proportionality.

Question 178

Explain why equal increases in load do not produce equal increases in extension beyond the limit of proportionality. [4]

Answer 

The internal structure of the material responds differently under higher loads. The proportional relationship no longer holds, so extension increases more rapidly.

Question 179

A student says, “The limit of proportionality occurs at the highest point of the graph.”

(a) State whether this is correct. [1]

(b) Explain your answer. [3]

Answer 

(a) Incorrect.

(b) The limit of proportionality is where the graph stops being a straight line, not necessarily the highest load shown.

Question 180

Discuss why understanding the limit of proportionality is important in engineering applications. [6]

Answer 180

Engineers need materials that behave predictably under load. Below the limit of proportionality, calculations based on Hooke’s law are accurate. Operating beyond this limit leads to unpredictable behavior. Understanding this limit ensures safe and reliable design.

Question 181

(a) State the equation linking force, mass and acceleration. [1]

(b) Define acceleration. [2]

(c) State the unit of acceleration. [1]

Answer 

(a) F = ma

(b) Acceleration is the rate of change of velocity.

(c) Metres per second squared (m/s²).

Question 182

A resultant force of 15 N acts on a mass of 3 kg.

(a) Calculate the acceleration. [3]

(b) State the direction of acceleration relative to the force. [2]

Answer 

(a)

a = F / m

a = 15 / 3

a = 5 m/s²

(b) The acceleration is in the same direction as the force.

Question 183

A trolley of mass 4 kg accelerates at 2 m/s².

(a) Calculate the resultant force acting on the trolley. [3]

(b) State the direction of acceleration if the force acts forward. [1]

Answer 

(a)

F = ma

F = 4 × 2

F = 8 N

(b) Forward.

Question 184

Explain how increasing the mass of an object affects its acceleration when the same force is applied. [4]

Answer 

From a = F / m, if force remains constant and mass increases, acceleration decreases. A heavier object accelerates less than a lighter object for the same force.

Question 185

A car of mass 1000 kg accelerates at 3 m/s².

(a) Calculate the resultant force acting on the car. [3]

(b) State what would happen to the acceleration if the force doubled. [2]

Answer 

(a)

F = ma

F = 1000 × 3

F = 3000 N

(b) The acceleration would double.

Question 186

(a) Define mass. [2]

(b) Explain how mass is related to inertia. [2]

Answer 

(a) Mass is the amount of matter in an object.

(b) Objects with greater mass have greater inertia and are harder to accelerate.

Question 187

A force acts opposite to the direction of motion of a moving object.

(a) What effect does this have on speed? [2]

(b) Explain why this is still considered acceleration. [3]

Answer 

(a) The object slows down.

(b) Acceleration is change in velocity. Since velocity decreases, acceleration occurs in the opposite direction to motion.

Question 188

A force of 20 N acts on a mass of 5 kg.

(a) Calculate the acceleration. [3]

(b) If the mass is reduced to 2.5 kg with the same force, calculate the new acceleration. [3]

Answer 

(a)

a = 20 / 5

a = 4 m/s²

(b)

a = 20 / 2.5

a = 8 m/s²

Question 189

Explain why acceleration is always in the same direction as the resultant force. [4]

Answer

From F = ma, acceleration is directly proportional to force. Since mass is positive, acceleration must have the same direction as the force.

Question 190

A force of 30 N produces an acceleration of 6 m/s².

Calculate the mass of the object. [3]

Answer 

m = F / a

m = 30 / 6

m = 5 kg

Question 191

A cyclist of mass 80 kg accelerates at 1.5 m/s².

(a) Calculate the resultant force. [3]

(b) Explain what would happen if air resistance increased. [3]

Answer 

(a)

F = ma

F = 80 × 1.5

F = 120 N

(b) Increased air resistance reduces the resultant force, decreasing acceleration.

Question 192

Explain the motion of an object when the resultant force acting on it is zero. [4]

Answer 

From F = ma, if F = 0, then a = 0. With zero acceleration, the object remains at rest or moves at constant speed in a straight line.

Question 193

A car accelerates forward. Friction and air resistance act backward.

Explain how F = ma applies in this situation. [5]

Answer 

The driving force acts forward while friction and air resistance act backward. The resultant force equals driving force minus resistive forces. According to F = ma, this resultant force produces forward acceleration.

Question 194

Describe an experiment to verify F = ma. [6]

Answer 

• Place a trolley on a smooth track.
• Attach a hanging mass over a pulley.
• Measure acceleration using a timer or motion sensor.
• Increase the hanging mass to increase force.
• Observe that acceleration increases with force.
• Increase trolley mass and observe acceleration decreases.

Question 195

A 2 kg object moves in a circle at constant speed.

(a) Is it accelerating? [1]

(b) Explain using F = ma. [4]

Answer 

(a) Yes.

(b) Its direction changes continuously, so velocity changes. Therefore acceleration exists. A resultant force towards the centre produces this acceleration.

Question 196

Explain why force is required to change direction but not to maintain constant velocity. [4]

Answer 

Constant velocity means no change in velocity, so acceleration is zero. From F = ma, zero acceleration means zero resultant force. A change in direction changes velocity, requiring a resultant force.

Question 197

A rocket of mass 500 kg experiences a thrust force of 6000 N upward and weight of 4900 N downward.

(a) Calculate the resultant force. [3]

(b) Calculate the acceleration. [3]

Answer 

(a)

Resultant force = 6000 − 4900

= 1100 N upward

(b)

a = F / m

a = 1100 / 500

a = 2.2 m/s² upward

Question 198

Explain why a light ball accelerates more than a heavy ball when kicked with the same force. [4]

Answer 

From a = F / m, with the same force, a smaller mass produces a larger acceleration.

Question 199

A student says, “Acceleration always means speeding up.”

(a) State whether this is correct. [1]

(b) Explain your answer. [4]

Answer 

(a) Incorrect.

(b) Acceleration is change in velocity. It can mean speeding up, slowing down, or changing direction.

Question 200

Discuss the importance of F = ma in understanding motion and engineering applications. [6]

Answer 

F = ma explains how forces cause changes in motion. It shows that acceleration depends on force and mass. Engineers use it to design vehicles, calculate braking forces, and ensure safety. It underpins transport systems, machinery design, and structural safety calculations.

Question 201

(a) State Newton’s First Law of Motion. [3]

(b) Define inertia. [2]

Answer 

(a) An object remains at rest or continues to move at constant speed in a straight line unless acted upon by a resultant force.

(b) Inertia is the tendency of an object to resist changes in its state of rest or uniform motion.

Question 202

Explain why a book resting on a table does not move. [4]

Answer 

The weight of the book acts downward and the normal reaction force from the table acts upward. These forces are equal and opposite, so the resultant force is zero. According to Newton’s First Law, the book remains at rest.

Question 203

A ball rolls across the ground and eventually stops.

Explain this using Newton’s First Law. [4]

Answer 

Friction acts opposite to the direction of motion, producing a resultant force. This force changes the motion of the ball, causing it to slow down and stop. Without friction, the ball would continue moving at constant speed.

Question 204

State Newton’s Second Law of Motion. [3]

Answer

The acceleration of an object is directly proportional to the resultant force acting on it and inversely proportional to its mass.

Question 205

(a) Write the equation representing Newton’s Second Law. [1]

(b) State the units of each quantity. [3]

Answer 

(a) F = ma

(b) Force in newtons (N)

        Mass in kilograms (kg)

        Acceleration in metres per second squared (m/s²)

   

Question 206

A 6 kg object accelerates at 2 m/s².

Calculate the resultant force. [3]

Answer 

F = ma

F = 6 × 2

F = 12 N

Question 207

A force of 40 N acts on a 10 kg object.

Calculate the acceleration. [3]

Answer 

a = F / m

a = 40 / 10

a = 4 m/s²

Question 208

Explain why a larger mass produces a smaller acceleration for the same force. [4]

Answer

From a = F / m, acceleration is inversely proportional to mass. If mass increases while force remains constant, acceleration decreases.

Question 209

A car accelerates forward.

Explain why the acceleration is in the same direction as the resultant force. [4]

Answer 

Newton’s Second Law states that acceleration is proportional to the resultant force. Therefore, acceleration always occurs in the same direction as the force.

Question 210

Describe how Newton’s Second Law explains braking in a vehicle. [5]

Answer 

When brakes are applied, a frictional force acts opposite to motion. This produces a backward resultant force. According to F = ma, this causes backward acceleration, reducing the vehicle’s speed.

Question 211

State Newton’s Third Law of Motion. [3]

Answer 

When two objects interact, they exert forces on each other that are equal in magnitude and opposite in direction.

Question 212

State four characteristics of action–reaction forces. [4]

Answer 

• Equal in magnitude
• Opposite in direction
• Act on different objects
• Occur at the same time

Question 213

Explain why action–reaction forces do not cancel each other out. [4]

Answer

They act on different objects. Forces only cancel when acting on the same object.

Question 214

Describe how walking is explained by Newton’s Third Law. [5]

Answer

When you walk, your foot pushes backward on the ground. The ground pushes forward on your foot with an equal and opposite force. This forward force moves you forward.

Question 215

Explain rocket motion using Newton’s Third Law. [5]

Answer

Hot gases are expelled downward from the rocket. This is the action force. The gases exert an equal and opposite force upward on the rocket. This reaction force pushes the rocket upward.

Question 216

Describe recoil using Newton’s Third Law. [4]

Answer 

When a gun fires a bullet forward, the bullet exerts a force backward on the gun. The forces are equal and opposite, causing the gun to recoil.

Question 217

Explain how Newton’s First and Second Laws are related. [4]

Answer 

The First Law describes motion when resultant force is zero. The Second Law explains what happens when a non-zero resultant force acts, producing acceleration.

Question 218

A 1000 kg car experiences a driving force of 4000 N and resistive forces of 3000 N.

(a) Calculate the resultant force. [2]

(b) Calculate the acceleration. [3]

Answer 

(a) 4000 − 3000 = 1000 N

(b) a = F / m

a = 1000 / 1000

a = 1 m/s²

Question 219

Explain why heavy trucks accelerate more slowly than small cars. [4]

Answer 

Heavy trucks have larger mass. For the same force, acceleration is smaller because a = F / m.

Question 220

Explain how inertia is related to mass. [3]

Answer 

Mass measures inertia. Larger mass means greater resistance to changes in motion.

Question 221

Describe how balanced forces relate to Newton’s First Law. [4]

Answer 

Balanced forces produce zero resultant force. According to the First Law, an object remains at rest or moves at constant velocity.

Question 222

A cyclist turns a corner at constant speed.

Explain why this involves acceleration. [4]

Answer 

The direction of velocity changes. Since acceleration is change in velocity, acceleration occurs towards the center of the turn.

Question 223

Explain why acceleration does not always mean speeding up. [4]

Answer 

Acceleration is change in velocity. It can mean slowing down or changing direction as well as increasing speed.

Question 224

A 5 kg object accelerates at 3 m/s².

Calculate the force required. [3]

Answer 

F = ma

F = 5 × 3

F = 15 N

Question 225

Describe how Newton’s laws apply to a falling object in air. [6]

Answer 

Weight acts downward and air resistance acts upward. Initially weight is greater, so acceleration occurs downward. As speed increases, air resistance increases. Eventually forces balance and the object falls at constant speed.

Question 226

Explain how seatbelts relate to Newton’s First Law. [4]

Answer

Passengers continue moving forward due to inertia when a car stops suddenly. Seatbelts apply a force to stop them safely.

Question 227

A student claims heavier objects exert larger action forces.

Explain why this is incorrect. [4]

Answer 

According to the Third Law, forces between interacting objects are equal in magnitude regardless of mass.

Question 228

Explain how Newton’s Second Law is used in vehicle design. [4]

Answer 

Engineers calculate forces required for acceleration and braking. They design engines and braking systems using F = ma to ensure safety and performance.

Question 229

Describe the difference between the three laws in one sentence each. [6]

Answer

First Law: Describes motion when forces are balanced.

Second Law: Relates force to acceleration and mass.

Third Law: Describes forces between interacting objects.

Question 230

Explain why a force is required to change direction but not to maintain constant velocity. [4]

Answer 

Constant velocity means no acceleration, so no resultant force is required. Changing direction changes velocity, requiring acceleration and thus a resultant force.

Question 231

A 2 kg mass accelerates at 6 m/s².

Calculate the force acting. [3]

Answer 

F = ma

F = 2 × 6

F = 12 N

Question 232

Explain how Newton’s laws explain pushing a stalled car. [5]

Answer 

A push provides a forward force. If greater than friction, a resultant force causes acceleration. Once moving, balanced forces allow constant velocity.

Question 233

Explain why forces occur in pairs. [4]

Answer 

Forces arise from interactions between two objects. Each object exerts a force on the other, producing equal and opposite forces.

Question 234

A rocket expels gas downward at high speed.

Explain using all three laws. [6]

Answer 

According to Newton’s First Law, an object remains at rest or continues moving at constant velocity unless acted upon by a resultant force. A rocket on the launch pad will remain at rest unless a net upward force acts on it. When the engines are ignited, gases are expelled downward, creating a force that can overcome the rocket’s weight. Once the upward thrust becomes greater than the downward force of gravity, there is a resultant upward force and the rocket accelerates upward.

According to Newton’s Second Law, acceleration is proportional to the resultant force and inversely proportional to mass. The rocket accelerates upward because the thrust force produced by expelling gas downward is greater than the gravitational force acting on it. The greater the thrust, the greater the acceleration. As the rocket burns fuel, its mass decreases, so for the same thrust, the acceleration increases.

According to Newton’s Third Law, for every action there is an equal and opposite reaction. The action force is the rocket pushing gases downward at high speed. The reaction force is the gases pushing the rocket upward with an equal magnitude force in the opposite direction. This upward reaction force is called thrust and is responsible for lifting the rocket into the air.

Question 235

Explain how friction relates to Newton’s First Law. [4]

Answer 

Friction is a resistive force that acts between two surfaces in contact and always opposes the direction of motion or attempted motion. When an object moves across a surface, friction acts in the opposite direction, producing a resultant force that reduces the object’s velocity. According to Newton’s laws of motion, a resultant force causes acceleration, and in the case of friction, this acceleration is negative, meaning the object slows down. As friction continues to act, kinetic energy is gradually converted into heat energy, and the object eventually comes to rest. For example, when a car’s brakes are applied, friction between the brake pads and the wheels, as well as between the tyres and the road, creates a force opposite to motion, causing the car to decelerate and stop.

Question 236

A bus suddenly accelerates forward.

Explain passenger motion using Newton’s laws. [5]

Answer 

When a bus suddenly accelerates forward, passengers appear to move or fall backward. This can be explained using Newton’s Laws of Motion.

According to Newton’s First Law, a body at rest remains at rest unless acted upon by a resultant force. Before the bus moves, both the bus and the passengers are at rest. When the bus accelerates forward, a forward driving force acts on the bus due to the engine and friction between the tyres and the road. However, the passengers’ bodies tend to remain at rest because of inertia. The lower part of the body, in contact with the seat or floor, is pushed forward by the bus, while the upper part resists the change in motion. As a result, passengers lean or fall backward relative to the bus.

According to Newton’s Second Law, acceleration occurs when there is a resultant force. The bus accelerates because the forward driving force is greater than resistive forces such as friction and air resistance. Passengers only accelerate forward once a forward contact force from the seat or floor acts on them. The size of this force determines how quickly they accelerate with the bus.

According to Newton’s Third Law, when the seat pushes the passenger forward, the passenger pushes the seat backward with an equal and opposite force. These interaction forces explain how the passenger is brought into motion along with the bus.

Question 237

Calculate acceleration if a 50 N force acts on 25 kg. [3]

Answer 

a = F / m

a = 50 / 25

a = 2 m/s²

Question 238

Explain why rockets work in space without air. [4]

Answer 

Rockets are able to work in space even though there is no air because they do not rely on air to produce thrust. Their motion is explained by Newton’s Third Law of Motion.

A rocket carries both its fuel and an oxidiser, so it does not need oxygen from the air for combustion. When the fuel burns, hot gases are produced and expelled backward at very high speed through the rocket nozzle. According to Newton’s Third Law, when the rocket pushes the gases backward, the gases push the rocket forward with an equal and opposite force. This reaction force is called thrust.

Since this action and reaction force pair occurs between the rocket and the expelled gases, air is not required. In fact, rockets can work more efficiently in space because there is no air resistance to oppose their motion. As long as the thrust produced is greater than any opposing forces, such as gravity near a planet, the rocket will accelerate according to Newton’s Second Law.

Question 239

Describe how Newton’s laws apply to turning a car. [5]

Answer 

When a car turns, its motion can be explained using all three of Newton’s Laws of Motion.

According to Newton’s First Law, an object moving in a straight line will continue in that straight line unless acted upon by a resultant force. A moving car naturally tends to keep travelling straight due to inertia. When the driver turns the steering wheel, the tyres change direction, but the car would still continue straight unless a sideways force acts on it.

This sideways force is provided by friction between the tyres and the road. According to Newton’s Second Law, a resultant force causes acceleration. In circular motion, acceleration occurs towards the centre of the curve, even if the speed remains constant. This is called centripetal acceleration. The frictional force towards the centre of the turn provides the centripetal force needed to change the direction of the car’s velocity. The greater the speed or the sharper the turn, the greater the required centripetal force.

According to Newton’s Third Law, when the tyres push sideways against the road, the road pushes back on the tyres with an equal and opposite force. This reaction force acts towards the centre of the turn and allows the car to follow a curved path. Without sufficient friction, such as on an icy road, the car would skid because the necessary centripetal force would not be available.

Question 240

Explain why a moving object does not need a force to keep moving. [4]

Answer 

A moving object does not need a force to keep moving at constant velocity because of Newton’s First Law of Motion. This law states that an object will remain at rest or continue moving with constant speed in a straight line unless acted upon by a resultant force.

This means that force is only required to change motion, not to maintain it. If no resultant force acts on a moving object, its velocity will remain constant. In everyday life, objects eventually slow down because resistive forces such as friction and air resistance act in the opposite direction of motion. These forces create a resultant force that reduces speed.

If all resistive forces were removed, for example in deep space where there is negligible friction, a moving object would continue travelling at the same speed and in the same direction without any additional force. Therefore, force is needed to accelerate, decelerate, or change direction, but not to keep an object moving at constant velocity..

Question 241

Define resultant force. [2]

Answer

Resultant force is the single force that has the same effect as all the forces acting on an object combined. It is found by adding all the forces acting on the object, taking their directions into account.

If forces act in the same direction, they are added together. If they act in opposite directions, they are subtracted. When the resultant force is zero, the forces are balanced and the object remains at rest or moves with constant velocity. When the resultant force is not zero, the forces are unbalanced and the object accelerates in the direction of the resultant force.

Question 242

State the condition for zero acceleration. [2]

Answer 

The condition for zero acceleration is that the resultant force acting on the object is zero.

When all the forces acting on an object are balanced, the net force is zero. According to Newton’s Second Law, acceleration is proportional to the resultant force. Therefore, if the resultant force is zero, the acceleration is zero. The object will either remain at rest or continue moving with constant velocity in a straight line.

Question 243

Explain motion of a falling parachutist before and after parachute opens. [6]

Answer 

The motion of a falling parachutist can be explained using forces and Newton’s Laws of Motion.

Before the parachute opens, two main forces act on the parachutist: weight acting downward and air resistance acting upward. Just after jumping, weight is much greater than air resistance, so there is a resultant downward force. According to Newton’s Second Law, this causes the parachutist to accelerate downward. As speed increases, air resistance also increases. Eventually, air resistance becomes equal to weight. At this point, the resultant force becomes zero, so acceleration stops and the parachutist continues to fall at a constant speed called terminal velocity.

After the parachute opens, the surface area increases greatly, causing a sudden large increase in air resistance. Air resistance now becomes greater than weight, producing a resultant upward force. This does not make the parachutist move upward, but it reduces the downward velocity, meaning the parachutist decelerates. As the speed decreases, air resistance decreases until it once again becomes equal to weight. The forces are balanced, acceleration becomes zero, and the parachutist falls at a new, much lower terminal velocity until landing safely.

Question 244

A 3 kg object experiences 9 N resultant force. Calculate acceleration. [3]

Answer

Using Newton’s Second Law:

$$F = ma$$

Rearranging to find acceleration:

$$a = \frac{F}{m}$$

Substitute the given values:

$$a = \frac{9}{3}$$$$a = 3 \text{ m/s}^2$$

Acceleration = 3 m/s²

Question 245

Explain why action–reaction forces are equal. [4]

Answer 

Action and reaction forces are equal because of Newton’s Third Law of Motion, which states that when two objects interact, they exert forces on each other that are equal in magnitude and opposite in direction.

When object A exerts a force on object B, object B simultaneously exerts a force back on object A. These forces arise from the same interaction and occur at the same time. Since they are part of a single interaction pair, nature ensures that the force one object applies is matched by an equal force in return.

However, these forces do not cancel each other out because they act on different objects. For example, when you push against a wall, you apply a force on the wall, and the wall applies an equal and opposite force on you. The equality of these forces ensures conservation of momentum in interactions and explains how motion changes during collisions or propulsion.

Question 246

State one example of each Newton’s Law in daily life. [6]

Answer 

Newton’s First Law (Law of Inertia):

When a car suddenly stops, passengers move forward. Their bodies tend to continue in motion due to inertia until a force, such as the seatbelt, stops them.

Newton’s Second Law:

Kicking a football harder makes it accelerate more. A greater force produces a greater acceleration, provided the mass remains the same.

Newton’s Third Law:

When you jump off the ground, you push the ground downward, and the ground pushes you upward with an equal and opposite force, allowing you to rise into the air.

Question 247

A 1200 kg car travels at constant speed along a straight road.

(a) State the resultant force acting on the car. [1]

(b) Explain your answer using Newton’s First Law. [3]

Answer

(a) The resultant force acting on the car is 0 N.

(b) According to Newton’s First Law of Motion, an object will remain at rest or continue moving with constant velocity in a straight line unless acted upon by a resultant force. Since the car is travelling at constant speed along a straight road, its velocity is not changing. This means there is no acceleration.

If there is no acceleration, the resultant force must be zero. Therefore, the driving force of the engine is balanced by resistive forces such as friction and air resistance, resulting in a net force of zero.

Question 248

Define inertia. [2]

Explain why a fully loaded truck has greater inertia than an empty truck. [2]

Answer 

Inertia is the tendency of an object to resist any change in its state of rest or motion. It is the property of matter that makes an object remain at rest or continue moving with constant velocity unless acted upon by a resultant force.

Inertia depends on mass. A fully loaded truck has a greater mass than an empty truck, so it has greater inertia. This means it resists changes in motion more strongly, requiring a larger force to start moving, stop, or change direction.

Question 249

A force of 18 N acts on a 6 kg object.

(a) Calculate the acceleration. [3]

(b) State the direction of acceleration relative to the force. [1]

Answer 

(a)

a = F / m

a = 18 / 6

a = 3 m/s²

(b) In the same direction as the force.

Question 250

A 5 kg trolley is pulled forward with a force of 25 N. Friction is 10 N.

(a) Calculate the resultant force. [2]

(b) Calculate the acceleration. [3]

Answer 

(a) 25 − 10 = 15 N

(b)

a = F / m

a = 15 / 5

a = 3 m/s²

Question 251

Explain why passengers move forward when a bus stops suddenly. [4]

Answer 

When a bus stops suddenly, passengers move forward due to inertia.

According to Newton’s First Law of Motion, an object in motion will continue moving with constant velocity unless acted upon by a resultant force. When the bus is moving, both the bus and the passengers are travelling forward at the same speed. If the bus suddenly stops, a braking force acts on the bus through the tyres and road, bringing it to rest.

However, the passengers’ bodies tend to continue moving forward because of inertia. The lower part of the body, in contact with the seat, is slowed down by a force from the seat, but the upper body continues moving forward momentarily. This causes passengers to lurch forward until a force, such as the seatbelt or the seat in front, stops them.

Question 252

A rocket has a mass of 800 kg and experiences a thrust of 10 000 N upward. Its weight is 7800 N downward.

(a) Calculate the resultant force. [2]

(b) Calculate the acceleration. [3]

Answer 

(a) 10 000 − 7800 = 2200 N upward

(b)

a = F / m

a = 2200 / 800

a = 2.75 m/s² upward

Question 253

Explain why rockets can move in space where there is no air. [4]

Answer

Rockets can move in space even though there is no air because they do not rely on air to produce thrust. A rocket carries both its fuel and an oxidiser, so combustion can occur without oxygen from the atmosphere.

When the fuel burns, hot gases are produced and expelled backward at very high speed. According to Newton’s Third Law of Motion, when the rocket pushes the gases backward, the gases push the rocket forward with an equal and opposite force. This reaction force is called thrust.

Since the action and reaction forces occur between the rocket and the expelled gases, air is not required. As long as the thrust is greater than opposing forces such as gravity, the rocket will accelerate according to Newton’s Second Law.

Question 254

Describe recoil using Newton’s Third Law. [4]

Answer 

When a bullet is fired forward, it exerts a force on the gun. The gun exerts an equal and opposite force on the bullet. The backward force causes recoil.

Question 255

Explain why recoil of a gun is much smaller than the speed of the bullet. [4]

Answer 

Recoil can be explained using Newton’s Third Law of Motion, which states that for every action there is an equal and opposite reaction.

When a gun is fired, the expanding gases push the bullet forward out of the barrel. This forward force on the bullet is the action. At the same time, the bullet and gases exert an equal and opposite force backward on the gun. This backward force causes the gun to move in the opposite direction, which is called recoil.

The action and reaction forces are equal in magnitude but act on different objects. Because the gun has a much greater mass than the bullet, its backward acceleration is much smaller, which is why it moves back only slightly compared to the forward motion of the bullet.

Thank You!

Sana Shariq

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