Q147 / 150 · MHT CET 2025 (27 Apr Shift 2) · Physics
A solid sphere is in purely rotational motion about its diameter. The ratio of its angular momentum and kinetic energy is $\frac{\pi}{22}$. Find angular velocity of the sphere. ( $\pi=22 / 7$ )
- Correct answerA$10 \mathrm{rad} / \mathrm{s}$
- B$7 \mathrm{rad} / \mathrm{s}$
- C$14 \mathrm{rad} / \mathrm{s}$
- D$21 \mathrm{rad} / \mathrm{s}$
Solution
Angular momentum and rotational kinetic energy relate through the moment of inertia $I = \frac{2}{5}MR^2$ and angular velocity $\omega$ as $L = I\omega$ and $K = \frac{1}{2}I\omega^2$ respectively.
The ratio simplifies to $\frac{L}{K} = \frac{I\omega}{\frac{1}{2}I\omega^2} = \frac{2}{\omega}$.
Given $\frac{L}{K} = \frac{\pi}{22}$, we equate $\frac{2}{\omega} = \frac{\pi}{22}$.
Solving for angular velocity: $\omega = \frac{44}{\pi}$.
Substituting $\pi = \frac{22}{7}$ yields $\omega = 44 \times \frac{7}{22} = 14$ rad/s.
The angular velocity is therefore $14$ rad/s.
Hence, the correct answer is option: 'A'.