Two students are on a balcony a distance h above the street. One student throws a ball vertically downward at a speed vi at the same time the other student throws a ball vertically upward at the same speed. Answer the following symbolically in terms of vi g h and t. (a) What is the time interval between when the first ball strikes the ground and the second ball strikes the ground? (b) Find the velocity of each ball as it strikes the ground. (c) How far apart are the balls at a time t after they are thrown and before they strike the ground?