Question

A wheel is rotating at $ 900\,\,rpm $ about its axis. When the power is cut off it comes to rest in $ 1\min $ . The angular retardation in $ rad/{{s}^{2}} $ is

• A. $ \pi /3 $
• B. $ \pi /2 $
• C. $ \pi /6 $
• D. $ \pi /8 $

Answer 1

The Correct Option is B

$n=900\, rpm =\frac{900}{60} rps =15 rps$ $\therefore t=1\, \min =60\, s$ From equation of angular motion, we have $\omega=\omega_{0}-\alpha t$ $\therefore \omega=2 \pi n-\alpha t$ $\Rightarrow 0=2 \pi(15)-\alpha(60)$ $\Rightarrow \alpha=\frac{30 \pi}{60}=\frac{\pi}{2} rad / s ^{2}$