Impulse and force-momentumEdexcel A-Level Physics: Subtopic test

1. 1
   A tennis ball of mass 0.058 kg approaches a racket horizontally at 20 m s⁻¹. It is in contact with the strings for 5.0 ms and leaves the racket in the opposite direction at 30 m s⁻¹.

   (a)

   What is the change in momentum of the ball?

   [1 mark]

   • A1.2 kg m s⁻¹
   • B0.58 kg m s⁻¹
   • C2.9 kg m s⁻¹
   • D1.7 kg m s⁻¹

   (b)

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

   [1 mark]

   • A5.8 × 10² N
   • B0.58 N
   • C1.5 × 10⁻² N
   • D15 N

   (c)

   The ball has the same incoming and outgoing speeds, but a different racket keeps the ball in contact for longer. Explain the effect on the average force on the ball.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A driver of mass 70 kg, wearing a seat belt, is travelling at 15 m s⁻¹ when the car hits a wall. The seat belt and an airbag bring the driver to rest in 0.12 s.

   (a)

   What is the magnitude of the impulse on the driver?

   [1 mark]

   • A4.7 N s
   • B8.4 N s
   • C8.8 × 10³ N s
   • D1.1 × 10³ N s

   (b)

   Which statement best explains why the airbag reduces the risk of serious injury?

   [1 mark]

   • AIt reduces the driver's change of momentum.
   • BIt increases the time over which the driver's momentum changes, so the average force is smaller.
   • CIt reduces the impulse on the driver, so less force is needed.
   • DIt increases the driver's change of momentum, so the force is spread out.

   (c)

   Calculate the average force on the driver while being stopped.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student investigates the relationship between force and change of momentum. A trolley of mass 0.800 kg moves towards a force sensor at 0.80 m s⁻¹, measured by a light gate, and rebounds at 0.55 m s⁻¹. The data logger connected to the sensor shows that the collision lasts 0.045 s and gives the impulse, found from the area under the recorded force against time, as 1.05 N s.

   (a)

   Calculate the change in momentum of the trolley. Compare it with the impulse given by the data logger and state whether the results support the relationship FΔt = Δp.

   [3 marks]

   (b)

   Calculate the average force on the trolley during the collision. Explain why the largest force recorded by the sensor is greater than this average force.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student investigates how the force on a trolley relates to its change of momentum, using a trolley of mass 0.250 kg, a track, a force sensor connected to a data logger, a light gate and an interrupt card. In one trial the trolley approaches the sensor at 1.60 m s⁻¹ and rebounds at 1.10 m s⁻¹, and the logger gives the impulse on the trolley as 0.72 N s.

   (a)

   Describe how the student could use the apparatus to investigate the relationship between the force on the trolley and its change in momentum, and how the results could be analysed.

   [6 marks]

   (b)

   Evaluate whether the results of this trial support the relationship FΔt = Δp, and suggest how the reliability of the investigation could be improved.

   [6 marks]

   Total for question 4: 12 marks

End of questions