# A weightlifter holds a barbell stationary above their head. They then lower the barbell slowly back down to the ground at a constant velocity. Explain, using Newton's laws, why the barbell moves at a constant velocity as it is lowered, and describe what happens to the forces acting on the barbell when it is first held stationary above the weightlifter's head.

> Eduqas A-Level Physics — 1.2 Forces and Newton's laws · Explain · 5 marks

> A weightlifter lifts a heavy barbell from the ground and holds it stationary above their head. They then lower it slowly back to the ground at a constant velocity.

## Mark scheme (5 marks)

1. When the barbell is held stationary, the forces acting on it are balanced (resultant force is zero).
2. The weight of the barbell acts downward and the upward force from the weightlifter's hands is equal in magnitude.
3. Newton's First Law states that an object remains stationary or moves at constant velocity when the resultant force acting on it is zero.
4. When the barbell is lowered at constant velocity, the forces on it are balanced / the resultant force is zero.
5. The upward force from the weightlifter's hands is less than the weight when stationary is compared to the lowering phase, OR correctly states that during lowering the weightlifter's hands exert an upward force equal to the weight of the barbell.

## Key terms

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

## Related

- [Revision notes for Eduqas A-Level Physics](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-weightlifter-holds-a-barbell-stationary-f7758fa5) · Published by Druglandscape Ltd.