# A student pushes a heavy box along a warehouse floor at a constant velocity. Explain why the box moves at a constant velocity even though the student is applying a force, and describe what would happen to the motion of the box if the student suddenly doubled their pushing force.

> OCR A-Level Physics B: Advancing Physics (H557) — 2.1 Physical quantities and units · Explain · 5 marks

> A student applies a horizontal pushing force to a heavy box resting on a concrete warehouse floor. The box moves at a constant velocity across the floor.

## Mark scheme (5 marks)

1. At constant velocity, the resultant force on the box is zero / the forces are balanced
2. The student's pushing force is equal to the friction force acting in the opposite direction
3. This is consistent with Newton's First Law: an object with zero resultant force continues at constant velocity
4. When the pushing force is doubled, a resultant force now acts on the box in the direction of motion (pushing force is greater than friction)
5. The box will accelerate / speed up (in the direction of the push), as stated by Newton's Second Law

## Key terms

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

## Related

- [Revision notes for OCR A-Level Physics B: Advancing Physics (H557)](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-student-pushes-a-heavy-box-69a25b28) · Published by Druglandscape Ltd.