Momentum and conservation of momentumEdexcel International A Level Physics: Subtopic test

1. 1
   A trolley of mass 0.80 kg moving at 1.5 m s⁻¹ along a level, friction-compensated track collides with a stationary trolley of mass 0.40 kg. In one run the two trolleys stick together on impact. In a second run they bounce apart instead.

   (a)

   What is the momentum of the 0.80 kg trolley before the collision?

   [1 mark]

   • A1.2 kg m s⁻¹
   • B0.53 kg m s⁻¹
   • C2.3 kg m s⁻¹
   • D0.90 kg m s⁻¹

   (b)

   In the run where the trolleys stick together, what is their common speed immediately after the collision?

   [1 mark]

   • A0.50 m s⁻¹
   • B1.5 m s⁻¹
   • C1.0 m s⁻¹
   • D3.0 m s⁻¹

   (c)

   In the second run the 0.80 kg trolley continues in the same direction at 0.50 m s⁻¹ after the collision. Calculate the velocity of the 0.40 kg trolley after the collision.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A rifle of mass 3.0 kg is held loosely and is initially at rest. It fires a bullet of mass 0.020 kg, which leaves the barrel with a speed of 400 m s⁻¹ horizontally.

   (a)

   What is the total momentum of the rifle and bullet just before the rifle is fired?

   [1 mark]

   • A8.0 kg m s⁻¹ forwards
   • B8.0 kg m s⁻¹ backwards
   • C3.0 kg m s⁻¹ forwards
   • Dzero

   (b)

   What is the recoil speed of the rifle?

   [1 mark]

   • A8.0 m s⁻¹
   • B2.7 m s⁻¹
   • C133 m s⁻¹
   • D0.0067 m s⁻¹

   (c)

   Explain, using Newton's third law, why the rifle recoils and why the total momentum after firing is still zero.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A tennis ball of mass 0.16 kg hits a vertical wall at right angles at a speed of 12 m s⁻¹. It rebounds along the same line with a speed of 8.0 m s⁻¹. The ball is in contact with the wall for 0.015 s.

   (a)

   Calculate the change in momentum of the ball.

   [3 marks]

   (b)

   Calculate the average force exerted by the wall on the ball. State the average force exerted by the ball on the wall, including its direction, and give the reason.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A car of mass 1200 kg travelling at 20 m s⁻¹ on a straight, level road runs into the back of a stationary van of mass 800 kg. The two vehicles lock together and move off as one. The collision is very short and the resistive forces on the vehicles during it are negligible. The car driver has a mass of 75 kg and wears a seat belt.

   (a)

   Explain how the principle of conservation of momentum and Newton's third law apply to this collision, and calculate the speed of the vehicles immediately after it.

   [6 marks]

   (b)

   The car driver slows from 20 m s⁻¹ to the speed of the car after the collision in 0.15 s. Without the seat belt and crumple zone the same change in speed would take place in 0.05 s. Evaluate how the time of the collision affects the force on the driver.

   [6 marks]

   Total for question 4: 12 marks

End of questions