Question

A uniform metre scale balances horizontally on a knife edge placed at $55\text{cm}$ mark when a mass of $25\text{g}$ is suspended from one end, then mass of the scale is

• A. $200\text{g}$
• B. $225\text{g}$
• C. $350\text{g}$
• D. $275\text{g}$

Answer 1

The correct option is B $225\text{g}$

The centre of gravity of a meter scale will be acting at the mid-point (i.e $50\text{cm})$ of the scale.

For the balance, the moment of forces on both sides of knife edge should be equal.
Therefore,
Anticlockwise moment = Clockwise moment
$\Rightarrow mg(55-50)=25g(100-55)$
$\Rightarrow m=\frac{25\times 45}{5}=225\text{g}$
Hence option (b) is correct.