Question

# The angular speed of a fly wheel making $120$ revolutions per minute isA.$\pi$ rad/sec.B.$2\pi$ rad/sec. C.$4\pi$ rad/sec.D.$4{\pi ^2}$ rad/sec.

Hint: The angular speed of a wheel is directly proportional to the frequency or the numbers of revolutions per minute/second.
Formula Used: Angular speed $\omega {\text{ = 2}} \times \pi \times \eta$ rad/sec.
Where $\eta$ is the frequency of the wheel.

Fly wheel makes$120$ revolutions per minute which is the frequency of the wheel ($\eta$).
So revolutions made by wheel per second ($\eta$)= $\dfrac{{120}}{{60}}$ =$2$
$\omega {\text{ = 2}} \times \pi \times \eta$
$\omega {\text{ = 2}} \times \pi \times 2$
$\omega {\text{ = 4}}\pi$
The angular speed of the wheel is $4\pi$ rad/sec.