Question

A thin circular disc of mass $m$ and radius $R$ is about its axis with a constant angular velocity has two masses each of mass $m$ (same mass of disc) at the opposite ends of a diameter disc. Now if the masses as are removed, the angular velocity of disc would be:-

• A. $\frac{w}{5}$
• B. $5w$
• C. $\frac{5}{2}w$
• D. $\frac{2}{5}w$

Answer 1

The correct option is B $5w$

$I_1{w}_1=I_2{w}_2$

$=\left(\frac{M{R}^2}{2}+M{R}^2\times 2\right)w=\left(\frac{M{R}^2}{2}\right)w^{\prime }$

$=\frac{5M{R}^2}{2}w=\frac{M{R}^2}{2}{w}^{\prime }$

$=w^{\prime }=5w$

Hence,

option $\left(B\right)$ is correct answer.