Q. A wheel of moment of inertia $5 \times 10^{- 3}kg - m^{2}$ is making 20 revolutions/sec. The torque required to stop it in $10\ sec$ is

A) $2\pi \times 10^{- 2}N - m$
B) $2\pi \times 10^{2}N - m$
C) $4\pi \times 10^{- 2}N - m$
D) $4\pi \times 10^{2}N - m$
Explanation

(a) $\alpha = \frac{2\pi(n_{2} - n_{1})}{t} = \frac{2\pi(0 - 20)}{10} = - 4\pi\ rad/s^{2}$
Negative sign means retardation
Now $\tau = I\alpha = 5 \times 10^{- 3} \times 4\pi = 2\pi \times 10^{- 2}N - m$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.