posted by obinna .
Suppose that you lob the ball with an initial speed of v = 16.1 m/s, at an angle of θ = 51.9° above the horizontal. At this instant your opponent is d = 11.2 m away from the ball. He begins moving away from you 0.400 s later, hoping to reach the ball and hit it back at the moment that it is h = 2.06 m above its launch point. With what minimum average speed must he move? (Ignore the fact that he can stretch, so that his racket can reach the ball before he does.)