The diameter of a disc is `1m`. It has a mass of `20kg`. It is rotating about its axis with a speed of `120` rotations in one minute. Its angular momentum in `kg m^2//s` is

Options

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

Answer

B

Explanation

120 rpm = 2rps
`rArr omega = 2pi (2)= 4pi rad s^(-1)`
`therefore` Angular momentum,
`L = I omega`
`= ((Mr^(2))/(2))omega= (((20)(0.5)^(2))/(2))(4pi)`
`= 3.14 kgm^(2)s^(-1)`.