A block hangs motionless from an ideal vertical spring. It is then pulled downward so that the spring is stretched below its equilibrium length and released from rest. Which of the following best describes the direction of the block’s acceleration at the instant it is released?
(a) Downward, because the block’s initial velocity is downward.
(b) Neither upward nor downward, because the acceleration is zero whenever the velocity is zero.
(c) Upward, because the upward spring force exceeds the block’s weight at that instant.
(d) Downward, because the block’s weight is always greater than the spring force whenever the spring is stretched.