The lob in tennis is an effective tatic when your opponent is near the net. It c

Question

The lob in tennis is an effective tatic when your opponent is near the net. It 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 degrees 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 it 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.)

Explanation / Answer

vertical component of balls speed=15*sin 50=11.49 m/s vertical height reached=2.1 m let time taken be t. horizontal distance=10 m i.e. 15*cos 50 * t=10 so t=1.0371 sec time left for the opponent to reach there=1.0371-0.3=1.0071 sec so his velocity=10/1.0071=9.9295 m/s

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