A string is wrapped around the rim of a wheel of moment of interia $0.20\mathrm{kg}-{\mathrm{m}}^2$ and radius 20cm . The wheel is free to rotate about its axis is fixed . Initially, the wheel is at rest. The string is now pulled by a force of 20 N . The angular velocity of the wheel 5.0 seconds is $\mathrm{n}\times {10}^2\mathrm{rad}/\sec .$ Then value of n is: