A flywheel is in the form of a uniform circular disc of radius `1 m` and mass `2 kg`. The work which must be done on it to increase its frequency of rotation from `5` to `10 rev//s` is approximately

Options

A. `1.5 xx 10^(2) J`
B. `3.0 xx 10^(2) J`
C. `1.5 xx 10^(3) J`
D. `3.0 xx 10^(3) J`

Answer

C

Explanation

W = change in rotational kinetic energy `= (1)/(2)I(omega_(f)^(2)-omega_(i)^(2))`
`=(1)/(2)((1)/(2)mR^(2))[(2pif_(f))^(2)-(2pif_(i))^(2)]`
`=(1)/(4)xx2xx(1)^(2)xx4xxpi^(2)(100-25)`
`= 4.48 xx 10^(3) J ~~ 1.5 xx 10^(3)J`.