Question

A uniform half metre rule balances horizontally on a knife edge at 29 cm mark when a weight of 20 gf is suspended from one end. 

(i) Draw a diagram of the arrangement. 

(ii) What is the weight of the half metre rule?

Answer 1

(i) Let the weight of the half metre rule be x gf and it acts at the 25 cm mark (centre of gravity).

 

(ii) Anti-clockwise moment (ACWM) =  x * 4 gf cm 

Clockwise moment (CWM) = 20 x 21 gf cm 

In equilibrium,

The weight of the half metre rule is 105 gf.