A ball is dropped vertically from a height d above the ground. It hits the ground and bounces up vertically so height d2. Neglecting subsequent motion and air resistance, its velocity v varies with the height h above the ground is

For the given condition initial height h = d and velocity of the ball is zero. When the ball moves downward its velocity increases and it will be maximum when the ball hits the ground & just after the collision it becomes half and in opposite direction. As the ball moves upward its velocity again decreases and becomes zero at height d2. This explanation match with graph (1).