Question

A meter scale is pivoted at its mid point and a 50 g mass suspended from the 20 cm mark. What mass balances the ruler when suspended from 65 cm mark?

Answer 1

Let mass 'm' be suspended from 65 cm mark so as to balance the metre scale. 

In balanced condition.

sum of clockwise moments = sum of anticlockwise moments

50 x (50 - 20) = m x (65 - 50)

or, 50 x 30 = m x 15

or, m = `1500/15` = 100g