# A train travels from one city to another city and then returns to the starting city. Explain why the train's displacement at the end of the journey is zero, even though its average speed during the journey is not zero.

> Cambridge International IGCSE Physics (0625) — 1.2 Motion · Explain · 4 marks

## Mark scheme (4 marks)

1. Displacement measures the overall change in position / distance in a given direction from start to finish
2. The train returns to its starting position, so its final position equals its initial position
3. Average speed is calculated using total distance travelled (not displacement), which is non-zero
4. Distance is a scalar quantity so it does not cancel when the direction reverses, whereas displacement is a vector so the return journey cancels the outward journey

## Key terms

- [displacement](https://www.gradenine.co.uk/glossary/displacement)
- [average speed](https://www.gradenine.co.uk/glossary/average-speed)

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- [Revision notes for Cambridge International IGCSE Physics (0625)](https://www.gradenine.co.uk/learn)
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Source: [GradeNine](https://www.gradenine.co.uk/q/a-train-travels-from-one-city-bf9d53d6) · Published by Druglandscape Ltd.