Question

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 the metre stick is

• A. $56\,g$
• B. $66\,g$
• C. $76\,g$
• D. $86\,g$

Answer 1

Answer: (B)

$66\,g$

Answer 2

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 $10 g(45-12) = mg (50-45);$ $10g \times 33 = mg \times 5$ $m = \frac{10 \times 33}{5} = 66\,g$