Question

A circular solid disc of uniform thickness 20 mm, radius 200 mm and mass 20 kg, is used as a flywheel. If it rotates at 600 rpm, the kinetic energy of the flywheel, in joules is

• A. 395
• B. 790
• C. 1580
• D. 3160

Answer 1

The correct option is B 790

$KE=\frac{1}{2}I{\omega }^2$
$I=\frac{m{r}^2}{2}=\frac{20\times (0.2{)}^2}{2}$
$I=0.4kg{m}^2$ $\omega =\frac{2\pi N}{60}=\frac{2\times \pi \times 600}{60}$ $=62.83\frac{rad}{s}$ $\therefore KE=\frac{1}{2}\times 0.4\times (62.83{)}^2=790J$