1. 1
   A skateboarder is travelling in a straight line across a flat, level skate park at a constant velocity of 4 m/s. The skateboarder, including their skateboard, has a total mass of 60 kg.

   (a)

   Which equation is used to calculate the momentum of the skateboarder?

   [1 mark]

   • Ap = m x v
   • Bp = m ÷ v
   • Cp = F x t
   • Dp = 1/2 x m x v^2

   (b)

   What is the momentum of the skateboarder?

   [1 mark]

   • A240 kg m/s
   • B56 kg m/s
   • C15 kg m/s
   • D64 kg m/s

   (c)

   State the SI unit of momentum, and explain why momentum is described as a vector quantity rather than a scalar quantity.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In a railway shunting yard, wagon A (mass 5000 kg) rolls along a straight, frictionless track at a constant velocity of 3 m/s towards a stationary wagon B (mass 2000 kg). The two wagons collide and couple together, moving off as a single combined mass.

   (a)

   What is the total momentum of the two-wagon system immediately before the collision?

   [1 mark]

   • A6000 kg m/s
   • B15000 kg m/s
   • C21000 kg m/s
   • D35000 kg m/s

   (b)

   According to the principle of conservation of momentum, what is the total momentum of the combined wagons immediately after the collision?

   [1 mark]

   • AZero, because wagon B was stationary before the collision
   • BLess than before the collision, because energy is lost as heat and sound
   • CThe same as before the collision, 15000 kg m/s
   • DGreater than before the collision, because the two wagons have combined

   (c)

   Calculate the common velocity of the two wagons immediately after they couple together.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A tennis ball of mass 0.058 kg travels horizontally towards a player's racket at a velocity of 30 m/s. The racket is in contact with the ball for 0.0050 s, after which the ball rebounds horizontally away from the racket at a velocity of 25 m/s in the opposite direction. Take the ball's initial direction of travel as positive.

   (a)

   Calculate the change in momentum of the tennis ball during its contact with the racket.

   [3 marks]

   (b)

   Calculate the average force exerted by the racket on the ball during the 0.0050 s contact time, and state the direction in which this force acts.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A car manufacturer is developing safety features for a new car model, including a front crumple zone, a driver's airbag and seatbelts fitted with pretensioners. During a head-on collision, the car's momentum changes very quickly from a high value to zero as it comes to a stop. The manufacturer wants to explain to safety inspectors how these features work together to protect occupants, and how the same crash would affect a much more massive object such as a fixed concrete safety barrier.

   (a)

   Explain, using ideas about momentum, impulse and force, how the crumple zone, airbag and seatbelt pretensioners work together to reduce the risk of injury to the occupants of the car during a head-on collision.

   [6 marks]

   (b)

   Evaluate, using Newton's third law and the principle of conservation of momentum, what happens during the collision if the car strikes a stationary concrete safety barrier of very large mass that is fixed to the ground. In your answer, compare the change in velocity of the car with the change in velocity of the barrier.

   [6 marks]

   Total for question 4: 12 marks

End of questions