Question

A disc of mass 2 kg and radius 0.2 m is rotating with angular velocity 30 rad/s. What is angular velocity, if a mass of 0.25 kg is put on the periphery of the disc?

• A. 24 rad/s
• B. 36 rad/s
• C. 15 rad/s
• D. 26 rad/s

Answer 1

The correct option is A 24 rad/s

Let the final angular velocity be $w$.

Applying conservation of angular momentum : $L_f=L_i$

Or $\left(\frac{M_{disc}{R}^2}{2}w\right)+M_{particle}{R}^{2}w=\left(\frac{M_{disc}{R}^2}{2}\right)w_i+0$

Or $\frac{2\times {0.2}^2}{2}\times w+0.25\times {0.2}^2\times w=\left(\frac{2\times {0.2}^2}{2}\right)\times 30$

$⟹w=24rad/s$