A 0.450 kg block rests on a frictionless horizontal surface, where it is attached to a massless spring whose k-value equals 18.0 N/m. Let x be the displacement, where x = O is the equilibrium position and x > 0 when the spring is stretched. The block is pushed, and the spring compressed, until X; = -4.00 cm. It then is released from rest and undergoes simple harmonic motion. (a) What is the block's maximum speed (in m/s) after it is released? m/s (b) How fast is the block moving (in m/s) when the spring is momentarily compressed by 1.20 cm (that is, when x = m/s (c) How fast is the block moving (in m/s) whenever the spring is extended by 1.20 cm (that is, when passing through x = +1.20 cm)? m/s (d) Find the magnitude of the displacement (in cm) at which the block moves with one-half of the maximum speed. |x| = cm -1.20 cm)? =