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 12.0 cm mark, the stick is found to be balanced at 45.0 cm. What is the mass of the metre stick?

Options

A. 56 g
B. 66 g
C. 76 g
D. 86 g

Answer

B

Explanation

Let m be the mass of the metre stick concentrated at C , the 50 cm mark as shown in the figure

In equilibrium taking moments of forces about C , we get `10 g (45 - 12) = mg (50 - 45) implies 10 g xx 33 = mg xx 5`
`m = (10 xx 33)/(5) = 66`g