Practise Conservation of momentum. 14 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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Two ice skaters stand still, facing each other. They push each other away. Skater A has a mass of 60 kg and skater B has a mass of 45 kg. Friction is negligible. In which direction does skater B move?
In the opposite direction to skater A.
A trolley of mass 1.5 kg moves at 2.0 m/s. Calculate its momentum. Use the equation: momentum = mass × velocity
3.0 kg m/s
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy5 marks
(a) Complete the sentence. In a closed system, the total momentum before an event is ............ the total momentum after the event. Tick (✓) one box.[1]
greater than
equal to
less than
(b) A trolley of mass 2.0 kg moving at 3.0 m/s collides with a stationary trolley of mass 1.0 kg. Calculate the total momentum before the collision. Use the equation: momentum = mass × velocity[2]
(c) The trolleys stick together. Calculate their velocity after the collision.[2]
Show the answer and mark scheme
(a)Answer: equal to
(b)Answer: 6.0 kg m/s
p = 2.0 × 3.0 (+ 0)
6.0 (kg m/s)
(c)Answer: 2.0 m/s
6.0 = (2.0 + 1.0) × v
v = 2.0 (m/s)
Question 2Medium6 marks
Two ice skaters stand still, facing each other. They push each other away. Skater A has a mass of 60 kg and skater B has a mass of 45 kg. Friction is negligible.
(a) What is the total momentum of the skaters before they push? Give a reason for your answer.[2]
(b) After the push, skater A moves at 1.5 m/s. Calculate the velocity of skater B.[3]
(c) In which direction does skater B move?[1]
Show the answer and mark scheme
(a)Answer: Zero, because neither skater is moving.
zero
neither skater is moving / both velocities are zero
(b)Answer: 2.0 m/s (in the opposite direction to A) m/s
total momentum after = 0, so 60 × 1.5 = 45 × v
v = 90 ÷ 45
2.0 (m/s)
(c)Answer: In the opposite direction to skater A.
in the opposite direction to skater A
Question 3Hard9 marks
An astronaut is floating at rest outside a space station. The total mass of the astronaut and spacesuit is 110 kg. The astronaut throws a bag of tools, of mass 2.5 kg, directly away from the space station at 6.0 m/s.
(a) Calculate the velocity of the astronaut after throwing the bag.[3]
(b) Calculate the total kinetic energy of the astronaut and the bag after the throw.[3]
(c) Before the throw the total kinetic energy was zero. Where did the kinetic energy come from?[1]
(d) The astronaut is 12 m from the space station. Calculate the time taken for the astronaut to reach the space station.[2]
Show the answer and mark scheme
(a)Answer: 0.14 m/s towards the space station m/s
total momentum before = 0, so 110 × v = 2.5 × 6.0
v = 15 ÷ 110
0.14 (m/s) towards the space station
(b)Answer: 46 J
kinetic energy of the bag = 0.5 × 2.5 × 6.02 = 45 (J)
kinetic energy of the astronaut = 0.5 × 110 × 0.1362 = 1.0 (J)
total = 46 (J)
(c)Answer: The chemical energy store of the astronaut’s muscles.
the chemical energy store (of the astronaut’s muscles)