Q: A uniform disk of mass 300 kg is rotating freely about a vertical axis through its centre with constant angular velocity ω_{o} . A boy of mass 30 kg starts from the centre and moves along a radius to the edge of the disk. The angular velocity of the disk now is

(A) $\frac{\omega_0}{6}$

(B) $\frac{\omega_0}{5}$

(C) $\frac{4\omega_0}{5}$

(D) $\frac{5 \omega_0}{6}$

**Click to See Solution : **

$\displaystyle L = (0 + \frac{300R^2}{2})\omega_0 = (\frac{300R^2}{2} + 30 R^2)\omega $

$\displaystyle 150 \omega_0 = 180 \omega $

$\displaystyle \omega = \frac{5}{6}\omega_0 $