Interpreting the question in diagram form.

The diagram for any body should be drawn in the form.
if the body is uniform, its mass or weight will act from the centre of gravity which is obtained by,

image 249

i.e. For a uniform metre rule, which is marked from 0-100cm, the centre of gravity from which the mass or weight acts is,

image 250

Then the required value is calculated from the principle of moment.


A uniform metre rule is pivoted at 30cm mark. It balances horizontally when a body of mass 20g is suspended at 25cm mark.

a) Draw a force diagram for the arrangement.
b) Calculate the mass of the metre rule
(Ans: m=5g)

Example: 6 A uniform half-metre rule is pivoted at 15cm mark and balances horizontally when a body of 40g is hanging from 2cm mark.
i) Draw a diagram of the arrangement.
ii) Calculate the mass of the metre rule.
(Ans: m=52g)

Example: 7 A uniform rod AB of length 5cm is suspended at 2m from end A. if the mass of the rod is 10kg. Calculate the mass of the body, which must be suspended at 1m from end A so as for the rod to balance horizontally.
(Ans: m=5kg)

Example: 8 A hand cart of length 1.5 m, has the centre of gravity at length 0.5 m from the wheel when loaded with 50kg as shown below.

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If the mass of the hand cart is 10 kg, find the effort needed to lift the hand cart.