A stone is swinging in a horizontal circle 0.8 m in diameter, at 30 rev/min. A distant light causes a shadow of the stone to be formed on a nearby wall. What is the amplitude of the motion of the shadow? What is the frequency?
(a) 0.4 m, 1.5 Hz
(b) 0.4 m, 0.5 Hz
(c) 0.8 m, 0.5 Hz
(d) 0.2 m, 0.5 Hz