The diameter of a flywheel is 1 m. It has a mass of 20 kg. It is rotating about its axis with a speed of 120 rotations in one minute. Its angular momentum in kg m s' is

Options

A. `13.4`
B. `31.4`
C. `41.4`
D. `43.4`

Answer

B

Explanation

Here `d= 1 m epsilon = 120` rpm , M = 20 kg
`r = (d)/(2) = (1)/(2) m = 0.5` m
`omega = 2 pi epsilon = (2pi xx 120)/(60) = 4pi rad s^(-1)`
`therefore L = I omega = (Mr^(2))/(2) omega = (20 xx (0.5)^(2) xx 4pi)/(2)`
`=10 xx 0.25 xx 4 xx 3.14 = 31.4 kg m^(2) s^(-1)`