The diameter of a solid disc is 0.5 m and its mass is 16 kg. What torque will increase its angular velocity from zero to 120 ratations/minute in 8 seconds.

Explanation

Moment of inertia of the disc
`I = 1/2 MR^2 = 1/2 xx16xx[0.5/2]^2 =1/2 kg-m^2`
Angular velcoity ` omega = (120 xx2pi)/60 - 4 rad//s`
and change in angular momentum `Delta L = I omega - 0 = I omega `
`:." Angular impulse is " tau xx t = Delta rArr `
`tau = (Delta L)/t = 1/8 xx1/2xx4 pi =pi/4 N - m`