# A passenger train starts from rest at a station and speeds up along a straight track. After some time, the train travels at a constant velocity. Explain why the train's velocity stops increasing even though the engine continues to provide a driving force.

> OCR GCSE Physics A: Gateway Science (J249) — P2.1 Motion · Explain · 4 marks

> A train leaves a station and accelerates along a straight, level track. The engine provides a constant driving force throughout the journey. After a period of acceleration, the train reaches a constant velocity and no longer speeds up.

## Mark scheme (4 marks)

1. As the train speeds up, resistive forces (such as friction/air resistance/drag) increase
2. At constant velocity, the driving force equals the resistive forces (balanced forces / resultant force is zero)
3. Because the resultant force is zero, the train does not accelerate (Newton's First Law)
4. The train therefore continues at a constant (terminal) velocity

## Key terms

- [constant velocity](https://www.gradenine.co.uk/glossary/constant-velocity)

## Related

- [Revision notes for OCR GCSE Physics A: Gateway Science (J249)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-passenger-train-starts-from-rest-b65e2c45) · Published by Druglandscape Ltd.