Question

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 $12cm$ mark, the stick is found to be balanced at $45.0cm$ . What is the mass (in gram ) of the metre stick?

Answer 1

Answer: 66

Let total mass of the metre stick be $M$ gram

Distance between mid-point $E$ and new centre of gravity ( $DE$ ),
$=50-45=5cm$
Distance between $12cm$ mark and new centre of gravity ( $CD$ ),
$=45-12=33cm$
From the principle of moments in equilibrium,
$Mg\times DE=(2\times 5g)\times CD$
$M\times 5=10\times 33$
or $M=66g$
$\therefore$ Mass of the metre stick is $66g$ .