Question

A wheel is rotating at $900\text{rpm}$ about its axis. When power is cut off, it comes to rest in $60\text{s}$. The angular retardation is $\left(rad/s^2\right)$

• A. $\frac{\pi }{2}$
• B. $\frac{\pi }{4}$
• C. $\frac{\pi }{6}$
• D. $\frac{\pi }{8}$

Answer 1

The correct option is A $\frac{\pi }{2}$

${\omega }_i=30\pi$ $rad/s$
${\omega }_f=0$ $rad/s$
$t=60s$
Now,
as it is retardation
${\omega }_f={\omega }_i-\alpha t$
$0=30\pi -\alpha 60$
$\alpha =\frac{30\pi }{60}=\frac{\pi }{2}rad/s^2$