Moments (Edexcel A Level Physics): Exam Questions

A student used a force meter attached to one end of a uniform metre rule to determine the mass of a block. The centre of the metre rule is attached to a stand about which it can pivot.

A block of unknown mass $m$ can be attached to the metre rule through one of the small holes, as shown.

The student attached the block to each small hole and adjusted the force meter to make it vertical before taking a reading.

Explain how the student could check the metre rule is horizontal before taking a reading.

The student places the block at the $80\text{ cm}$ mark and pulls the force meter vertically downwards until the ruler is horizontal. The reading on the force meter is $1.45\text{ N}$.

Calculate the mass $m$ of the block. You should take moments about the pivot.

The student wants to reduce the percentage uncertainty in the value obtained for the mass of the block.

The student moved the force meter towards the centre of gravity of the metre rule and repeated the measurements.

Deduce whether the percentage uncertainty in the value obtained for the mass of the block is reduced by the student moving the force meter. No calculations are required.