A wheel having radius 10cm is coupled by a belt to another wheel of radius 30cm. ${\text{1}}^{\text{st}}$  wheel increases its angular speed from rest at a uniform rate of $1.57{\text{rads}}^{-2}$ . The time for ${\text{2}}^{\text{nd}}$  wheel to reach a rotational speed of $100\text{rev/min}$ is ….(assume that the belt does not slip)