Circular disc of mass 2 kg and radius 1 m is rotating about an axis perpendicular to its plane and passing through its centre of mass with a rotational kinetic energy of 8 J. The angular momentum is (Js) is

Options

A. 8
B. 4
C. 2
D. 1

Answer

B

Explanation

Rotational kinetic energy `= (1)/(2)I omega^(2)=8 J`
`rArr (1)/(2)xx(1)/(2)mr^(2)omega^(2)=8or (1)/(4)xx2xx(1)^(2)omega^(2)=8`
or `omega^(2)=16 or omega=4 "rad s"^(-1)`
Angular momentum, `L=Iomega=(1)/(2)mr^(2)omega`
`=(1)/(2)xx2xx(1)^(2)xx4=4"J-s"`.