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iPad 3:53 PM 57% edugen.wileyplus.com yLUGradebook Courses-Blackboard Learn tudy & Practice Assignment Gradebook ORION PRINTER VERSION BACK SOURCES chapter Chapter 03, Problem 77 The lob in tennis is an effective tactic 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 (see the drawing). Suppose that you loft the ball with an initial speed of 15.0 m/s at an angle of 50.0° the horizontal. At this instant your opponent is 10.0 m away from the ball. He begins moving away from you 0.49 s later, hoping to reach the ball and hit it back at the moment that it is 2.10 m above its launch point. With what minimum average speed must he move? (ignore the fact that he can stretch, so that his racket blemsT blem 10 blem 23launch blem 52can reach the ball before he does.) blem 71 blem 75 15.0 mis y Study 50.0 100 m the tolerance is +/-296 Click if you would like to Show Work for this question: Open Show Work Question Attempts: 0 of 5 used SAVE FOR LATER SUBMIT ANSWER Copyright 2000-2015 by John Wiley&Sons;, Inc. or related companies. All rights reserved. Version 4.16.17

Explanation / Answer

In vertical Using H = ut + at^2 /2

2.10 = (15sin50)t + (-9.81)t^2 /2

t = 2.14 sec

ball will reach at that point in 2.14 sec.

and horizontal distance traveled by ball = ux * t = 15cos50 * 2.14

d = 20.63 m

Now player has 2.14 - 0.49 = 1.65 sec to move 20.63 - 10 = 10.63 m .

so average speed = 10.63 / 1.65 = 6.44 m/s

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