Aball is dropped from rest from the top of a building and strikes the ground with a speed vf. from ground level, a second ball is thrown straight upward at the same instant that the first ball is dropped. the initial speed of the second ball is vo = vf, the same speed with which the first ball will eventually strike the ground. ignoring air resistance, decide whether the balls cross paths at half the height of the building, above the halfway point, or below the halfway point. give your reasoning.