A circular disc of radius \( R \) is free to rotate about an axis passing through its centre. An external tangential force \( F \) is applied on the disc along its edge. If the angular velocity of disc is increased from \( 0 \) to \( \mathrm{w} \) in a time \( \mathrm{t} \) then the work done by \( \mathrm{F} \) during same time \( t \) is