The questions are on the momentum test. Take it under real conditions before reading the mark scheme.
Quick answer: Momentum is the product of an object's mass and its velocity, p = mv, measured in kg m/s. This mark scheme gives the model answers and the marks for the 8 questions of the Physics 9-10 test on momentum, from momentum basics to catching a ball, with the equivalent answers to accept.
Use this marking scheme to score yourself. Award marks for a correct formula, a correct substitution and a correct final answer with unit and direction. Do not give the final mark if the unit or the sign is missing.
Level: Physics grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: HS-PS2-2, HS-PS2-3
Question 1 Momentum basics (2 marks)
- Momentum is mass multiplied by velocity (p = mv).
- The unit is kg m/s.
Marking: 1 mark for mass × velocity, 1 mark for the correct unit.
Question 2 Tennis ball (2 marks)
p = mv = 0.058 × 45 = 2.61, so 2.6 kg m/s.
Marking: 1 mark for the substitution, 1 mark for the answer with unit.
Question 3 Locking trolleys (3 marks)
Momentum before = 4.0 × 3.0 = 12 kg m/s. After: 6.0 × v = 12, so v = 2.0 m/s.
Marking: 1 mark for momentum before, 1 mark for equating to total mass × v, 1 mark for the answer with unit.
Question 4 Rifle recoil (3 marks)
Bullet momentum = 0.020 × 300 = 6.0 kg m/s. The rifle has equal momentum backwards: 4.0 × v = 6.0, so v = 1.5 m/s backwards.
Marking: 1 mark for the bullet momentum, 1 mark for equal and opposite momentum, 1 mark for the answer with direction.
Question 5 Force on a trolley (3 marks)
- Impulse = Ft = 30 × 0.40 = 12 N s.
- Δp = 12 kg m/s.
- v = 12 ÷ 6.0 = 2.0 m/s.
Marking: 1 mark for each part.
Question 6 Airbag (2 marks)
The driver’s momentum must fall to zero, and the airbag makes this take a longer time. Since F = Δp ÷ t, the same Δp over a longer time gives a smaller force.
Marking: 1 mark for longer stopping time, 1 mark for using F = Δp ÷ t to conclude the force is smaller.
Question 7 Opposite directions (3 marks)
- 2.0 × 4.0 + 3.0 × (−2.0) = 8.0 − 6.0 = +2.0 kg m/s.
- 2.0 + 3.0 = 5.0 kg.
- v = 2.0 ÷ 5.0 = 0.40 m/s to the right.
Marking: 1 mark for each part; deduct the first mark if the minus sign is missing.
Question 8 Catching a ball (2 marks)
Pulling the hands back increases the time over which the ball stops. The change in momentum is fixed, so the average force on the hands is smaller, and the catch hurts less.
Marking: 1 mark for longer time, 1 mark for smaller force because Δp is fixed.
