Question

A wheel having moment of inertia 2 kg-m­2 about its vertical axis, rotates at the rate of 60 rpm about this axis. The torque which can stop the wheel's rotation in one minute would be:

• A. $\frac{2\pi}{15}N - m$
• B. $\frac{\pi}{12}N - m$
• C. $\frac{\pi}{15}N - m$
• D. $\frac{\pi}{18}N - m$

Answer 1

Answer: (C)

$\frac{\pi}{15}N - m$

Answer 2

$\alpha = \frac{2\pi(n_{2} - n_{1})}{t} = \frac{2\pi\left( 0 - \frac{60}{60} \right)}{60} = \frac{- 2\pi}{60} = \frac{- \pi}{30}rad/\sec^{2}{}$

∴ $\tau = I\alpha = \frac{2 \times \pi}{30} = \frac{\pi}{15}N - m$