AQA AS Physics

Topic Questions

4.4 Newton’s Laws of Motion

1a2 marks

State Newton’s Second Law.

1b2 marks

At its launch, a rocket and its contents have a total mass of 150 000 kg.  The engine produces an upward thrust of 3 500 000 N.  Figure 1 below shows the rocket just after its launch. 

Figure 1

4-4-s-q--q1b-easy-aqa-a-level-physics

Calculate the weight of the rocket at the launch.

1c2 marks

Calculate the resultant force acting on the rocket during the launch.

1d2 marks

Calculate the acceleration of the rocket at launch.

Did this page help you?

2a4 marks

Figure 1 shows a skier being pulled forward by rope at a constant velocity along a horizontal section between two ski runs. The tension in the rope is 50 N and the total mass of the skier is 85 kg. 

Figure 1

4-4-s-q--q2a-easy-aqa-a-level-physics

State the name of each of the forces AD acting on the skier in Figure 1.

2b2 marks

Determine the magnitude of Force A and explain your answer.  

2c3 marks

The rope towing the skier suddenly brakes, so Force B no longer acts on the skier, however the skier continues to move forwards. 

Force A remains constant. 

By considering the horizontal forces now acting on the skier, explain whether the skier accelerates or decelerates after the tow rope breaks.

2d2 marks

Assuming the magnitude of Force A remains constant, as determined in part (b), calculate the deceleration of the skier.

Did this page help you?

3a2 marks

A remote-controlled racing car has a mass of 0.60 kg. It can accelerate uniformly from rest to 5.2 m s–1 in 1.6 s. 

Calculate the acceleration of the car.

3b2 marks

Calculate the resultant force acting on the car when it is accelerating.

3c2 marks

After 1.8 s the motor is switched off and the car decelerates uniformly until it stops.  The deceleration of the racing car is 0.80 m s–2.

Given that the resistive force is the only force acting on the car once the motor is switched off, calculate the magnitude of this force.

3d2 marks

Assuming that the resistive force was constant throughout the motion of the racing car, use your answer from part (b) to calculate the thrust from the motor when the racing car was accelerating.

Did this page help you?

4a2 marks

A brick of mass 1.5 kg is resting on the floor as shown in Figure 1.  

                                                                        Figure 1

4-4-s-q--q4a-easy-aqa-a-level-physics

Name the forces A and B acting on the block.

4b3 marks
(i)
State Newton’s first law
(ii)

Explain how Newton’s first law can be applied to the forces acting on the brick.

4c4 marks
(i)
State Newton’s third law 
(ii)
 Explain how Newton’s third law can be applied to the forces acting on the brick.  
4d2 marks

A horizontal force is applied to the brick which causes it to accelerate at 0.2 m s−2. 

Use Newton’s Second Law to calculate the size of the horizontal force which is applied to the brick.

Did this page help you?

5a2 marks

A block of wood of mass 5.2 kg, sitting on a smooth table, is acted upon by a force of 5.8 N as shown in Figure 1.   

Figure 1

4-4-s-q--q5a-easy-aqa-a-level-physics

Calculate the expected acceleration of the wooden block, assuming there are no frictional forces acting between the block and the table.

5b3 marks

The movement of the wooden block is investigated using a data logger. 

The velocity-time graph obtained by the data-logger is shown in Figure 2 below. 

Figure 2

4-4-s-q--q5b-easy-aqa-a-level-physics

Use the data in Figure 2 to calculate the actual acceleration of the wooden block.

5c2 marks

Use the actual acceleration of the block, calculated in part (b), to calculate the resultant force acting on the block.

5d2 marks

As the acceleration of the block in parts a) and b) are different, this shows that there is a resistive force acting between the block and the table.  

   Use your answer to part (c) to calculate the resistive force acting on the block 

   Remember that the block is being pulled with a force of 5.8 N.

Did this page help you?

1a3 marks

Figure 1 shows the motion of a truck as it moves on a curved track. 

Figure 1

4-4-s-q--q1a-hard-aqa-a-level-physics

The slope beyond B is horizontal. 

On the axes below, sketch a speed – time graph for the truck from its release at A until it reaches the position X shown in Figure 1. 

Indicate on your graph the time when the truck is at B.

4-4-s-q--q1a-fig-1-hard-aqa-a-level-physics

1b2 marks

Explain how Newton’s first law of motion is illustrated by the motion of the truck between B and X.

1c3 marks

Figure 2 shows another truck moving freely down a ramp inclined at an angle to the horizontal. 

Figure 2

4-4-s-q--q2a-hard-aqa-a-level-physics

The truck starts from rest at the top of the ramp and reaches point C. Friction and air resistance are negligible. 

Discuss how the acceleration of the truck in Figure 2 differs from the acceleration of the truck in Figure 1.

1d6 marks

Now both trucks are filled with water and travel, initially from rest, along a straight track.

The driving force on each truck remains constant. 

The total resistive forces acting on each truck increases with both speed and mass of the truck. A large proportion of the mass of each truck is due to the water they are carrying. 

Both trucks have the same initial mass. However, at the instant they begin to move, a large leak develops in one of the trucks and all the water leaks out during the journey. The shape of the speed-time graph for the truck without a leak is similar to the one drawn in part (a).

Discuss how the speed–time graph for the truck with the leak will be different from the graph of the truck without a leak. 

Your answer should include an explanation of: 

  • The shape of the graph
  • The effect of water loss on the initial gradient of the graph
  • The effect of water loss on the final speed of the truck 

You may draw on the figure below to help you with your answer. 

The quality of your written communication will be assessed in your answer.

4-4-s-q--q2d-hard-aqa-a-level-physics

Did this page help you?

2a6 marks

Two skateboarders X and Y are standing stationary on their skateboards as shown in Figure 1.

Figure 1

06Xarcac_4-4-s-q--q2a-hard-aqa-a-level-physics

When X holds the ball, they remain still. When X throws a ball to Y, they move to the left. When Y catches the ball, they move to the right and then eventually come to rest. 

Explain, using Newton’s three laws of motion, the motion of both skateboarders. 

Ignore all effects of friction and air resistance.

2b4 marks

Two people of the same mass are having a tug-of-war match. Each person tries to pull the other by leaning backwards, as shown in Figure 2. 

Figure 2

4-4-s-q--q2b-hard-aqa-a-level-physics

Describe, using Newton’s laws, the resultant motion of the people pulling on the rope. 

You may assume there is no friction.

2c3 marks

Both skateboarders X and Y have a mass of 65 kg and play tug-of-war, as shown in Figure 3. 

Figure 3

4-4-s-q--q2c-hard-aqa-a-level-physics

They hold opposite ends of 17 m of rope. X pulls on the rope and exerts a force of 40 N, whilst Y remains stationary. Friction is ignored. 

Show that it takes 7.4 seconds for both X and Y to meet.

2d3 marks

Figure 4 shows two people playing tug-of-war. Person A has a mass of 60 kg and person B has a mass 75 kg.

Figure 4

ed4zuokM_4-4-s-q--q2d-hard-aqa-a-level-physics

Both people have slightly different materials for the sole of their shoes. This means the overall friction force on person A is 420 N and 21 N on person B. The rope has a mass of 2 kg and both A and B pull with different forces. 

Show that the resultant acceleration of both person A, person B and the rope is 3 m s–2 to the left.

Did this page help you?

3a3 marks

The set-up below shows three objects m subscript 1, m subscript 2 and m subscript 3 accelerating to the left at an acceleration a due to an applied force F such that the masses m subscript 2 and m subscript 3 do not move relative to mass m subscript 1. 

The objects m subscript 2 and m subscript 3 are connected by an inextensible string that passes through a light, inextensible pulley as shown in Figure 1. 

Figure 1

4-4-s-q--q3a-hard-aqa-a-level-physics

Derive an expression for F in terms of m subscript 1, m subscript 2, m subscript 3 and g. 

You may assume all surfaces to be smooth and the effects of friction neglected in the question.

3b4 marks

Three boxes, X, Y and Z are on a horizontal conveyor belt. The conveyor belt has an effective mass of 20 kg and each of the box X, Y and Z has a mass of 15 kg. 

With the three boxes stationary with respect to the belt, the system consisting of the belt and the three boxes move together at a constant speed of 2.1 m s–1. There is a driving force of 90 N which remains constant with time acting on the belt. 

The resistive force on the “belt-boxes system” by the rollers is equal to the total mass of the system. 

The distance between adjacent boxes is 6.3 m. When each box reaches the right end, the box will be lifted off vertically as shown in Figure 2a. 

Figure 2a

4-4-s-q--q3b-hard-aqa-a-level-physics

Figure 2b shows the belt-boxes system before box X reaches the right end where it will be lifted. 

Figure 2b

4-4-s-q--q3b-fig-1-hard-aqa-a-level-physics

Draw a free-body diagram of the forces on the belt-boxes system in Figure 2b. Include any significant values in the diagram.

3c3 marks

Box X is lifted off right away when the belt starts moving. Boxes Y and Z remain stationary with respect to the belt as it starts to accelerate, as shown in Figure 3.

Figure 3

4-4-s-q--q3c-hard-aqa-a-level-physics

Calculate the speed of box Z just before it is lifted off the conveyor belt.

3d3 marks

Boxes X, Y and Z in Figure 4 are now on an inclined conveyor belt at 30º without rollers. The driving force of 90 N moves the boxes up the slope initially at a velocity of 2.1 m s–1. 

Figure 4

4-4-s-q--q3d-hard-aqa-a-level-physics

Calculate the time taken for box Z to move to the position of box Y. 

The mass of the belt and friction can be ignored.

Did this page help you?

4a4 marks

Videos of astronauts on the International Space Station are shared all over the world. Many science students excitedly watch as the astronauts float around their cabins, perform space walks and other duties. 

Weightlessness is a term used to describe the experience of astronauts in orbit. Many early students of science have misconceptions about this term, particularly, that it means an absence of gravity. In fact, weightlessness is an effect of the astronauts being in a state of constant free fall. 

   By referring to Newton’s laws of motion, discuss the term ‘weightlessness’ as applied to astronauts in orbit. 

In your answer, you may want to include:

  • The misconception of an absence of gravity
  • What it means to be in a state of constant free fall.
4b5 marks

Einstein considered the theoretical perspective of an astronaut in deep space and was able to come up with fundamental revisions to Newton’s ideas of gravity and acceleration. More specifically, Einstein realised that there was an equivalence between uniform acceleration and the gravitational field.  

Figure 1a shows an astronaut and a newton meter N in a spacecraft. The spacecraft is in deep space, extremely far from any other masses, and its engines are switched off, so it (and all its contents) has an acceleration a = 0 m s–2. The display on the newton meter shows a reading of 0.00 N. 

Figure 1a

4-4-s-q--q5b-fig1-hard-aqa-a-level-physics

The engines are switched on such that the spacecraft is given an acceleration a = 5 m s­–2 as shown in Figure 1b. As a result, the display on the newton meter shows a reading of 300.00 N. 

Figure 1b

4-4-s-q--q5b-fig2-hard-aqa-a-level-physics

(i)      Interpret the readings on the newton meter N in Figure 1a and Figure 1b.

(ii)
Use the readings on the newton meter to determine the weight of the astronaut on the surface of the Earth.

       

4c4 marks

The astronaut in Figure 1b is holding a tennis ball in hand 1.40 m above the ground of the spacecraft and lets it go at a time t = 0 s. 

Describe and explain the subsequent motion of the tennis ball from the perspective of the astronaut. 

Include any relevant calculations in your answer.

Did this page help you?

1a3 marks

A 9.0 N force and a 5.0 N force act on a body of mass 3.0 kg at the same time. 

Calculate the maximum and minimum accelerations that can be experienced by the body.

1b2 marks

A fairground ride ends with the car moving up a ramp at a slope of 25° to the horizontal as shown in Figure 1.

Figure 1

4-4-s-q--q1b-medium-aqa-a-level-physics

The car carrying its maximum load of passengers has a total weight of 9.7 kN. 

Show that the component of the weight acting parallel to the ramp is about 4.1 kN.

1c2 marks

The mass of the fully loaded car is 950 kg. 

Show that the force in part (b) will decelerate the car at about 4.3 m s–2.

1d3 marks

The ride owner decides to use a shorter ramp and to install brakes on the car. The additional decelerating force provided by these brakes is 3400 N. The car enters the ramp at 33 m s–1. 

Calculate the new stopping time.

Did this page help you?

2a2 marks

The Soyuz Spacecraft is used to transport astronauts to and from an orbiting space station. The spacecraft is made up of three sections as shown in Figure 1.

Figure 1

4-4-s-q--q2a-medium-aqa-a-level-physics

On leaving the space station the spacecraft is given an initial horizontal thrust of 2400 N. 

Calculate the initial acceleration of the spacecraft during the firing of the thruster engines.

2b2 marks

Newton’s Third Law refers to pairs of forces. 

State one way in which a pair of forces referred to in Newton’s Third Law are the same and one way in which a pair of forces are different.

2c1 mark

When the spacecraft returns to the Earth’s atmosphere the orbital module and the service module are separated from the descent module. This descent module has its speed greatly reduced by drag from the atmosphere. 

Figure 2 shows two of the forces acting on the descent module as it travels down through the atmosphere.

Figure 2

4-4-s-q--q2c-medium-aqa-a-level-physics

State one reason why the two forces shown in Figure 2 are not a pair of forces as referred to in Newton’s Third Law.

2d3 marks

In one particular descent, the descent module has its speed reduced to 7.5 m s–1 by parachutes. The descent module also releases its empty tanks and shield to reduce its mass by 2280 kg. 

A final speed reduction can be carried out by using engines which operate for a maximum time of 4.4 s. When the engines are in use, the resultant upward force on the descent module is 1.0 kN. The safe landing speed of the descent module is 5.0 m s–1. 

   Determine whether these engines are able to reduce the speed of the descent module to its safe value. 

   At these landing speeds atmospheric drag is negligible.

Did this page help you?

3a3 marks

A boy throws a ball vertically upwards with a velocity of 13 m s–1 and lets it fall to the ground. Figure 1 shows a graph of velocity against time for the first few seconds of the ball’s motion.

Figure 1

4-4-s-q--q3a-medium-aqa-a-level-physics

Sketch on Figure 1 the variation of the ball’s velocity relative to the ground. 

3b2 marks

Figure 2 shows the ball deforming as it contacts the ground, just at the point where it is stationary for an instant and has reached maximum deformation.

Figure 2

4-4-s-q--q3b-medium-aqa-a-level-physics

Explain how Newton’s third law of motion applies to Figure 2.

3c2 marks

A moment later the ball begins to move upwards. 

Explain why there is a resultant upward force on the ball in Figure 2.

3d2 marks

The ball has a mass of 65 g. 

Calculate the maximum force exerted by the ground the moment the ball comes into contact with it.

Did this page help you?

4a2 marks

A van of mass 2000 kg pulls a trailer of mass 400 kg with a driving force of 3550 N. The van and trailer accelerate at 1.1 m s–2. 

Calculate the resultant force on the van and trailer.

4b2 marks

Calculate the resistive force on the van and trailer.

4c3 marks

The resistive force acting on the trailer is equal to the resistive force acting on the van. 

Use this information to calculate the force with which the van pulls the trailer.

4d4 marks

When the van reaches its destination, a crate is lifted vertically from the trailer at a constant speed by a cable attached to a crane. 

With reference to one of Newton’s laws of motion, explain why the tension, T, in the cable must be equal to the weight of the crate. 

You may be awarded marks for the quality of written communication in your answer.

Did this page help you?

5a4 marks

Figure 1 shows a tram car travelling at a constant velocity along a horizontal road. 

Figure 1

4-4-s-q--q5a-medium-aqa-a-level-physics

Draw and labels arrows on Figure 1 representing the forces on the tram car.

5b3 marks

State which forces on the car, if any, are a Newton’s third law pair. Explain why the others are not.

5c2 marks

Explain, using Newton’s second law, the significance of the tram car travelling at constant velocity.

5d4 marks

The mass of the tram car is 20 000 kg. At a speed of 15 m s-1 the frictional force is 350 N and the force of air resistance is 510 N as it accelerates forward. The total resistive force is proportional to the square of the car’s speed. The tram initially travels at 15 m s–1.

Calculate the force of air resistance when the tram travels at 30 m s–1, 5 seconds later.

Did this page help you?