You have been asked to design a "ballistic spring system" to measure the speed of bullets. a spring whose spring constant k is is suspended from the ceiling. a block of mass m hangs from the spring. a bullet of mass m is fired vertically upward into the bottom of the block. the spring's maximum compression d is measured. find an expression for the bullet's speed, express your answer in terms of the variables m, m, k, d, and constant g.