Question

a metre stick is balanced at its cente(50 cm).when 2 coins each of mass 5 g are put one on the top of the other at the 12 cm mark it is found to be balanced at 45 cm.what is the mass of the stick??

Answer 1

Let W and W′ be the respective weights of the metre stick and the coin.



The mass of the metre stick is concentrated at its mid-point, i.e., at the 50 cm mark.

Mass of the meter stick = m’

Mass of each coin, m = 5 g

When the coins are placed 12 cm away from the end P, the centre of mass gets shifted by 5 cm from point R toward the end P. The centre of mass is located at a distance of 45 cm from point P.

The net torque will be conserved for rotational equilibrium about point R.



Hence, the mass of the metre stick is 66 g.