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 solid disc
`I=(1)/(2)MR^(2)=(1)/(2)xx16xx((0.5)/(2))=(1)/(2)`
Angular velocity, `omega=(120xx2pi)/(60)=4 pi` and charge in angular momentum, `DeltaL=Iomega-0=Iomega`
Angular impulse,`tauxxt=DeltaL`
`rArr tau=(Delta L)/(t)=(1)/(8)xx(1)/(2)xx4pi=(pi)/(4)"N-m"`.