A metre stick is balanced on a knife edge at its centre. When two coins, each of mass 5 g are put one on top of the other at the 12 cm mark, the stick is found to be balanced at 45 cm. The mass of metre stick is

Answer

`66`

Explanation

Let the 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
`MgxxDE=(2xx5g)xxCD`
`Mxx5=10xx33`
or `M=66g`
`:.` Mass of the metre stick is 66g.