Question

A flywheel (considered as uniform ring) of mass 60 kg, radius 25 cm is making 240 revolutions per minute. Its kinetic energy is :

• A. $40{\pi }^{2}J$
• B. $80{\pi }^{2}J$
• C. $120{\pi }^{2}J$
• D. $160{\pi }^{2}J$

Answer 1

The correct option is C $120{\pi }^{2}J$

Given
$m=60Kg$
$r=25cm=0.25m$
$n=240revpermin=\frac{240}{60}revpersec$
For a flywheel the kinetic energy is
$E=\frac{1}{2}m{r}^2{\omega }^2$
$E=\frac{1}{2}m{r}^2(2\pi n{)}^2$
$E=\frac{1}{2}60\times \left(0.25{)}^2\right(2\frac{240}{60}{)}^2{\pi }^2$
$E=\frac{1}{2}240{\pi }^2$
$E=120{\pi }^{2}J$