Deduce the relation between torque and moment of inertia.

Explanation

We know torque acting on particle under force `vecF` about an axis of rotation at a distance r is given by
`vectau=vecrxxvecF implies tau = rF sin theta`
If `theta=90^@ implies tau = tau F`
As `F=ma = malpha r implies tau = mr^2 alpha implies ` So `tau = Ialpha`
Which is required expression.