Ball a is dropped from the top of a building of height h at the same instant that ball b is thrown vertically upward from the ground. when the balls collide, they are moving n opposite directions, and the speed of a is twice the speed of b. at what height does the collision occur? (use any variable or symbol stated above as necessary.) both balls experience constant acceleration once they are �n flight. choose a coordinate system with the origin at the ground and the upward direction positive. when the balls collide they are at the same height above the ground.