A cyclist is travelling along a flat road at a steady speed. The cyclist then stops pedalling and gradually comes to a stop. Describe the forces acting on the cyclist whilst travelling at steady speed, and explain why the cyclist slows down and eventually stops after pedalling ceases.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
At steady speed the cyclist’s pedalling produces a driving force that balances the resistive forces (rolling friction, air resistance). The resultant force is therefore zero, so the cyclist moves at constant velocity (Newton’s first law). When the cyclist stops pedalling the driving force becomes zero. The resistive forces are now unbalanced and act opposite to the motion, giving a negative resultant force. This causes a negative acceleration, so the cyclist slows down and eventually comes to rest.
Examiner tips
- Show the balance of forces at constant speed; mention Newton’s first law for zero acceleration.
- Explain that stopping pedalling removes the driving force, leaving only resistive forces.
- Use the term ‘negative acceleration’ to link the unbalanced force to slowing down.
- Keep the answer concise – 5 marks can be earned with 3–4 short sentences.
Mark scheme (5 marks)
- At steady speed, the driving force (from pedalling) equals the resistive forces (friction/air resistance)
- At steady speed the resultant force is zero so the cyclist does not accelerate (Newton's First Law / constant velocity)
- When pedalling stops, the driving force is removed / becomes zero
- There is now a resultant force in the direction opposing motion (resistive forces are unbalanced / greater than driving force)
- This resultant force causes a deceleration (negative acceleration), so the cyclist slows down and stops
Key terms in this question
Related
- All AQA A-Level Physics (7408) revision notes →
- How to answer a "Describe and Explain" question →
- Decode the mark scheme abbreviations →
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