A fly wheel of mass 60 kg and radius 40 cm is revolving at 300 rpm, then its rotational K.E. is

Options

A. `(48)/(pi^(2))J`
B. `480 pi J`
C. `(48)/(pi)J`
D. `240 pi^(2)J`

Answer

D

Explanation

K.E. of rotation `=(1)/(2) I omega^(2)`
`=(1)/(2)((1)/(2)mR^(2))omega^(2)`
`=(1)/(4)mR^(2)(2pi n)^(2)=pi^(2)n^(2)m R^(2)`
`= pi^(2)((300)/(60))^(2)xx60xx(0.4)^(2)=240 pi^(2)J`