Calculate the `KE` of rotation of a circular disc of mass `1 kg` and radius `0.2 m` rotating about an axis passing through its centre and perpendicular to its plane. The disc is making `30//pi` rotations per minute.

Explanation

`E = ?, m = 1 kg, r = 0.2 m`,
`n = (30)/(pi) rpm = (30)/(60 pi)rps = (1)/(2pi)rps`,
`omega = 2pi n = 2pi xx (1)/(2pi) = 1 rad//s`
About the given axis, `M.I.` of disc
`I = (1)/(2) mr^(2) = (1)/(2) xx (0.2)^(2) = (1)/(50)kg m^(2)`
`K.E.` of rotation `= (1)/(2)I omega^(2) = (1)/(2) xx (1)/(50) (1)^(2)`
`= 0.01 J`