6. In an engine, a piston oscillates with simple harmonic motion so that its position varies according to the expression, X = 4.00 cos (4t + 11/4) where x is in centimeters and t is in seconds. (a) At t = 0, find the position of the piston. (b) At t = 0, find velocity of the piston. (c) At t = 0, find acceleration of the piston. (d) Find the period and amplitude of the motion