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GCSE Questions: Moments and Centre of Gravity

Q10. In a balancing game, wooden blocks are used to build a tower. The shape of the tower at the start of the game is arrangement A. During the game, some of the blocks are taken out and put on top of the tower as shown in arrangement B. This causes the centre of mass of the tower to change.

(a)

(i) State what is meant by the term ‘centre of mass’.

The centre of mass of an object is the point through which the weight of that object acts in a uniform gravitational field - it is the point where the mass is (thought to be) concentrated.

In a GCSE examination always quote whatever your syllabus says is the definition - papers are not always marked by physicists - and markers look for the 'quote' to give the mark.

[1 mark]

(ii) Give two reasons why the tower in arrangement B is less stable than the tower in arrangement A.

- the centre of mass is higher

- the base (area) is smaller / narrower

[2 marks]

(b) The diagram below shows a different arrangement for the wooden blocks.

 

A block was placed in position X and an identical block was placed in position Y at the same time. Explain why the tower did not fall over.

You should include reference to moments in your answer.

The blocks at X and Y create equal and opposite moments producing a resultant moment of zero from their addition.

or

The block at X creates an anticlockwise moment and this is balanced by an equal clockwise moment by the block at Y.

 

[2 marks]

[5 Marks TOTAL]