The position of a 0.30−kg object attached to a spring is described by x=(0.21 m)cos(0.7πt). (Assume t is in seconds.) (a) Find the amplitude of the motion. m (b) Find the spring constant. N/m (c) Find the position of the object at t=0.31 s. m (d) Find the object's speed at t=0.31 s. m/s