Help~An English physics problem!hope some on can solve it
The lob in tennis is an effective when your opponent is near the net.Is consists of lofting the ball over his head,forcing him to move quickly away from the net.Suppose that you loft the ball with an initial speed of 15.0m/s,at an angle of 50.0degree above the horizontal.At this instant your opponent is 10.0m away from the ball.He begins moving away from you 0.30s later,hoping to reach the ball and hit it back at the moment that it is 2.10m 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.)