A plank with a body of mass m placed on it starts moving straight up according to the law y = a (1 = cos cot), where y is the displacement from the initial position, w = 11 s-1. Find:
(a) The time dependence of the force that the body exerts on the plank if a = 4.0 cm; plot this dependence;
(b) The minimum amplitude of oscillation of the plank at which the body starts falling behind the plank;
(c) The amplitude of oscillation of the plank at which the body springs up to a height h = 50 cm relative to the initial position (at the moment t = 0).