A motor pulley of radius 4 cm turns at 1500 revolutions per minute.

With $\theta$ in radians, an arc is $s = r\theta$ and a sector has the area $A = \frac{1}{2}r^2\theta = \frac{1}{2}rs$. A rolling wheel moves $2\pi r$ in each turn. For $n$ revolutions each minute, $\omega = \frac{2\pi n}{60}$ rad/s, and a point on the rim moves at $v = r\omega$. Two pulleys joined by a belt share the speed of the belt, so $r_1\omega_1 = r_2\omega_2$.