A railway wagon moving along a track collides with a stationary wagon. After the collision, the two wagons join together and move as one. Describe what happens to the momentum of each wagon during the collision and explain how the conservation of momentum applies to this event.

AQA GCSE Physics (8463) — 4.5.7 Momentum (Phys only) · Describe and Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

The moving wagon loses momentum during the collision.
The stationary wagon gains momentum during the collision.
The total momentum before the collision equals the total momentum after the collision.
The momentum lost by the moving wagon is equal to the momentum gained by the stationary wagon.

Examiner tips

  • Use the verb ‘lose’ for the moving wagon and ‘gain’ for the stationary wagon. Show the equality of total momentum before and after. Mention that the loss equals the gain to emphasise conservation.

Common mistakes

  • Saying the moving wagon ‘gains’ momentum or the stationary wagon ‘loses’ momentum. Forgetting to state that the total momentum is unchanged. Not linking the loss of one wagon’s momentum to the gain of the other.

Mark scheme (4 marks)

  1. The moving wagon loses momentum (during the collision)
  2. The stationary wagon gains momentum (during the collision)
  3. The total momentum before the collision equals the total momentum after the collision
  4. The momentum lost by the moving wagon is equal to the momentum gained by the stationary wagon

Key terms in this question

momentum · conservation of momentum

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