A metre stick is balanced on a knife edge at its centre. When two coins, each of mass 5g are put one on top of the other at the 12.0 cm mark, the stick is found to be balanced at 45.0 cm. What is the mass of the metre stick?

Explanation

Since stick is in rotational equilibrium, the total torque of all the forces about the resultant .R. is zero. Taking the turning effects about the point of action of the resultant .R. we have
`10 g xx 3=mg xx 5`
on solving m = 66 g