Write the expression for work done by a force in a rotational motion of a body.

Explanation

Work done=`tautheta` where `tau` is torque and `theta` is angular displacement
For a small displacement `dW=taudtheta` , where `tau=tau_1+tau_2+………+tau_n`
and `tau_i=r_iF_i sinprop` where `prop` is the angle between `vecr_i` and `vecF_i`