GCSE Physics: Conservation of momentum

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1. State the principle of conservation of momentum.

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   In a closed system, the total momentum before an event is equal to the total momentum after the event.

2. In a ? system, total momentum before an event equals total momentum after the event.

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   closed

3. What condition must a system satisfy for momentum to be conserved?

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   It must be a closed system — no external forces act on it.

4. Give a common example of an event in which momentum is conserved.

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   A collision between two objects (e.g. two laboratory trolleys).

5. Two objects collide in a closed system. How does the total momentum after the collision compare with before?

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   It is the same — total momentum is conserved.

6. Write the momentum equation for two objects (A and B) colliding in a closed system.

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   mₐuₐ + mᵦuᵦ = mₐvₐ + mᵦvᵦ (total momentum before = total momentum after).

7. What is the total momentum of two objects that were both stationary before an explosion?

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   Zero — so after the explosion the momenta of the pieces are equal in size and opposite in direction, still totalling zero.

8. Name a piece of apparatus used to measure trolley speed in a momentum experiment.

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   A light gate (alternatives: data logger or ticker timer).

9. Why are light gates preferred over stopwatches for measuring trolley speeds in collision experiments?

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   They remove human reaction time, so the measured speeds (and calculated momenta) are more accurate.