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GCSE Questions: Moments and Centre of Gravity

Q12. The diagram shows the back of a lorry. The lorry is used to carry horses.

(a) The ramp is lowered by pulling on the rope or by pulling on the handle. The hinge acts as a pivot.

Explain why it is easier to lower the ramp by pulling on the rope rather than pulling on the handle.

A smaller force is required at the rope to produce the same moment because the perpendicular distance from the pivot/hinge to the line of action of the force is greater so a smaller force is required

[2 marks]

(b) When the ramp is lowered, work is done to stretch a spring on the side of the ramp. Elastic potential energy is stored in the stretched spring.

This diagram shows the ramp part way down in a balanced horizontal position.

With the ramp horizontal:

the moment caused by the weight of the ramp = 924 Nm

the spring is stretched by 0.250 m

Calculate the elastic potential energy stored in the stretched spring.

Use data from the diagram.

moment caused by the weight of the ramp = moment caused by stretched spring

924 = F x 0.15

F = 924/0.15

F = 6160 N

_ _ _ _ _ _ _ _ _ _

Elastic energy stored = ½ force x distance moved

Ee = ½ Fe

Ee = ½ x 6160 x 0.250

Ee = 770 J

OR

F = ke

6160 = k × 0.25

k = 6160/0.25

k = 24640 N/m

Ee = ½ ke2

Ee = ½ x 24640 x 0.252

Ee = 770 J

[6 marks]

[8 Marks TOTAL]