A cyclist travelling at high speed collides with a stationary bollard and comes to a sudden stop. Explain why a cyclist wearing a padded jacket is less likely to suffer serious injury than a cyclist wearing no padding, even though both cyclists experience the same change in momentum.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Padded cycling jackets contain thick foam layers that compress during an impact. Without padding, the cyclist's body stops almost instantly on contact with the bollard.
Model answer (4 marks)
The padded jacket increases the time over which the cyclist’s momentum changes when he stops.
The change in momentum (Δp) is the same for both cyclists.
Force equals the rate of change of momentum (F=Δp/Δt).
Because Δt is larger for the padded cyclist, the force on his body is smaller, so he is less likely to be seriously injured.
The change in momentum (Δp) is the same for both cyclists.
Force equals the rate of change of momentum (F=Δp/Δt).
Because Δt is larger for the padded cyclist, the force on his body is smaller, so he is less likely to be seriously injured.
Examiner tips
- Use the formula F=Δp/Δt to link time and force.
- Show that Δp is identical for both cyclists before explaining the effect of Δt.
- Keep the answer concise – 4 marks only.
- Mention that a smaller force reduces injury risk.
Common mistakes
- Confusing force with momentum – writing that the padded jacket changes the cyclist’s momentum.
- Failing to state that Δp is the same for both cyclists.
- Using the wrong equation (e.g., F=ma) instead of the impulse–force relationship.
Mark scheme (4 marks)
- The padded jacket increases the time over which the cyclist's momentum changes (comes to rest)
- The change in momentum is the same for both cyclists
- Force equals the rate of change of momentum (change in momentum divided by time)
- Therefore, the padded jacket reduces the force experienced by the cyclist, reducing the risk of injury
Key terms in this question
Related
- All Pearson Edexcel International GCSE Physics (4PH1) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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