Rotational Motion: JEE Main 2011 Physics question

A pulley of radius $2$ $m$ is rotated about its axis by a force $F = \left( {20t - 5{t^2}} \right)$ newton (where $t$ is measured in seconds) applied tangentially. If the moment of inertia of the pulley about its axis of rotation is $10kg$-${m^2}$ the number of rotation made by the pulley before its direction of motion is reversed, is: