A circular disc is rotating about its own axis at a uniform angular velocity `omega`. The disc is subjected to uniform angular retardation by which its angular velocity is decreased to `omega/2` during `120` rotations. The number of rotations further made by it before coming to rest is

Options

A. 120
B. 60
C. 40
D. 20

Answer

C

Explanation

`alpha ` is constant ,
` alpha = (omega_(1)^(2) - omega_(2)^(2))/(2theta) = (omega - (omega/2)^(2) )/(2theta_(1)) = ((omega/2)^(2)-0)/(2theta_(2))`
`theta_(2) = (theta_(1))/3 `