AQA AS Physics

Topic Questions

4.4 Newton’s Laws of Motion

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

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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.

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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

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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

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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.

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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

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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

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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.

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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.

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5a4 marks

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

Figure 1

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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.

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