Q. A disc of moment of inertia 5 kg- $m^{2}$ is acted upon by a constant torque of 40 Nm. Starting from rest the time taken by it to acquire an angular velocity of 24 ${rads}^{- 1}$ is

A) 3 s
B) 4 s
C) 2.5 s
D) 120 s
Explanation

(a) Torque is defined as rate of change of angular momentum
$\therefore$ $\tau = \frac{dJ}{dt} = \frac{d(I\omega)}{dt}$
Given, $\tau = 40\ Nm,\ I = 5\ kgm^{2},\ \omega = 24\ rads^{- 1}$
$dt = \frac{d(I\omega)}{\tau} = \frac{5 \times 24}{40} = 3\ $s

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

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