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GCSE Questions: Moments and Centre of Gravity

Q7. Two children visit a playground.


(a) The diagram shows the two children, Margery and Johnny, sitting on a see-saw.

(i) The weight of each of the children creates a moment about the pivot.

What is meant by 'the moment of a force'?

[1 mark]

(ii) Give the unit for the moment of a force.

[1 mark]

(iii) The see-saw is balanced. What does that tell us about the size of the moment from Johnny, compared to the moment from Margery?

[1 mark]

(iv) Margery's weight is 400 N. Calculate Johnny's moment about the pivot point.

[3 marks]

(b) Johnny now sits on a swing as shown below. The swing is not moving.

Which arrow, J, K or L, points to the centre of mass of the child?

[1 mark]

(c) The child on the swing is now moving backwards and forwards like a pendulum. The frequency of the swing is 0.5 hertz. Calculate the periodic time of the swing.

[2 marks]

[9 Marks TOTAL]