Momentum, impulse and collisionsAQA A-Level Physics: Subtopic test

1. 1
   On a level laboratory track, a trolley of mass 0.80 kg moves at 1.5 m s⁻¹ towards a stationary trolley of mass 0.40 kg. The trolleys collide and stick together. Friction is negligible.

   (a)

   What is the total momentum of the two trolleys before the collision?

   [1 mark]

   • A0.60 kg m s⁻¹
   • B1.5 kg m s⁻¹
   • C1.2 kg m s⁻¹
   • D1.8 kg m s⁻¹

   (b)

   What is the speed of the trolleys immediately after the collision?

   [1 mark]

   • A1.0 m s⁻¹
   • B0.75 m s⁻¹
   • C1.5 m s⁻¹
   • D1.2 m s⁻¹

   (c)

   Show that the collision is inelastic.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A footballer kicks a stationary ball of mass 0.43 kg. The ball leaves the boot at 24 m s⁻¹ in a straight line. The boot and ball are in contact for 8.0 ms.

   (a)

   What is the magnitude of the impulse given to the ball?

   [1 mark]

   • A0.018 N s
   • B56 N s
   • C1300 N s
   • D10 N s

   (b)

   What is the average force exerted by the boot on the ball?

   [1 mark]

   • A0.083 N
   • B1300 N
   • C83 N
   • D10 N

   (c)

   The footballer kicks a softer ball of the same mass so that it also leaves at 24 m s⁻¹, but the contact time is 16 ms. State and explain what happens to the average force.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A courier packs a camera of mass 1.5 kg in a box lined with foam. The box is dropped and lands on a hard floor, so that the camera is travelling at 4.0 m s⁻¹ just before it is brought to rest by the foam in 0.020 s. Assume the average resultant force on the camera is much greater than its weight and that the camera does not rebound.

   (a)

   Explain how the foam lining reduces the risk of the camera being damaged when the box lands.

   [3 marks]

   (b)

   Calculate the average resultant force on the camera while it is stopped by the foam. Calculate also the average force if the same camera were brought to rest in 0.0020 s by a rigid box with no foam.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A road-safety regulator is assessing the risk of a car running into the back of a stationary lorry. In a model collision a car of mass 1200 kg travelling at 20 m s⁻¹ hits a stationary lorry of mass 8000 kg. The two vehicles lock together and move off as one. The collision lasts 0.12 s.

   (a)

   Calculate the average force exerted on the car during the collision.

   [6 marks]

   (b)

   The regulator argues that safety design must consider the people in both vehicles. Using the idea of conservation of momentum, evaluate the safety of the occupants of the car compared with the lorry driver, and discuss how vehicle design can reduce harm.

   [6 marks]

   Total for question 4: 12 marks

End of questions