Momentum and conservation of linear momentumEdexcel A-Level Physics: Subtopic test

1. 1
   Two trolleys, A and B, each of mass 0.60 kg, are on a straight horizontal track where friction is negligible. Trolley A moves to the right at 1.5 m s⁻¹ towards trolley B, which moves to the left at 1.5 m s⁻¹. Take movement to the right as positive.

   (a)

   What is the momentum of trolley A?

   [1 mark]

   • A0.40 kg m s⁻¹ to the right
   • B2.1 kg m s⁻¹ to the right
   • C0.45 kg m s⁻¹ to the right
   • D0.90 kg m s⁻¹ to the right

   (b)

   What is the total momentum of the two trolleys before they collide?

   [1 mark]

   • A1.8 kg m s⁻¹ to the right
   • B0.90 kg m s⁻¹ to the right
   • C0
   • D0.90 kg m s⁻¹ to the left

   (c)

   The trolleys collide and stick together. Deduce their velocity immediately after the collision, giving a reason.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student of mass 55 kg stands on a skateboard of mass 3.0 kg, at rest on smooth level ground. She throws a medicine ball of mass 4.0 kg horizontally forwards so that it leaves her hands at 5.0 m s⁻¹ relative to the ground.

   (a)

   What is the total momentum of the student, skateboard and ball before the ball is thrown?

   [1 mark]

   • A20 kg m s⁻¹ forwards
   • BZero
   • C5.0 kg m s⁻¹ forwards
   • D20 kg m s⁻¹ backwards

   (b)

   What is the speed of the student and skateboard immediately after the throw?

   [1 mark]

   • A0.34 m s⁻¹
   • B0.36 m s⁻¹
   • C0.081 m s⁻¹
   • D5.0 m s⁻¹

   (c)

   Explain, using Newton's laws, why the student moves backwards when she throws the ball.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A railway truck of mass 8000 kg rolling at 3.0 m s⁻¹ along a straight level track collides with a stationary truck of mass 12 000 kg. The trucks couple together and move off as one.

   (a)

   Calculate the velocity of the coupled trucks immediately after the collision.

   [3 marks]

   (b)

   Calculate the change in momentum of each truck. Explain how your answers are linked to Newton's third law.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student investigates collisions on a horizontal runway. Trolley A has mass 1.5 kg and trolley B has mass 0.50 kg. B is initially stationary and A is pushed towards it at 2.0 m s⁻¹.

   (a)

   Describe how the student could use light gates to test the principle of conservation of linear momentum, and how the investigation can be made reliable.

   [6 marks]

   (b)

   After the collision A moves on at 1.0 m s⁻¹ in the same direction. Calculate the velocity of B predicted by conservation of momentum. The student measures B's velocity as 2.7 m s⁻¹. Evaluate whether this result supports the conservation of momentum.

   [6 marks]

   Total for question 4: 12 marks

End of questions