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 mas 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

10g (45-12) = mg (50-45)

10 g × 33 = mg × 5

$m = \frac{10 \times 33}{5} = 66g$