Topic Menu

Cyber-chess a chess instruction site

GCSE Questions: Moments and Centre of Gravity

Q8. The diagram below shows how two forks can be used to make a potato balance on the end of a knife.

(a)

(i) Use a cross to mark the centre of mass of the arrangement in the diagram.

The cross needs to be on the knife as that is the midline. You got the mark for any position in the red area shown above.

[1 mark]

(ii) State the meaning of 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.

The Physics syllabus says it is 'that point at which the mass of the body may be thought to be concentrated'. That is because we can draw the weight arrow (representing the weight of the whole object) from that point. However the weight isn't really concentrated there - there is just an even distribution of weight on either side of that point.

[1 mark]

(b) The potato is tilted to one side and then released. The potato and forks then oscillate from side to side. The time taken for half an oscillation is 0.4 seconds.

Calculate the frequency of the oscillations.

T = 2 x 0.4s

f = 1/T

f = 1/0.8

f = 1.25 Hz

[3 marks]

[5 Marks TOTAL]