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Homework Help: Couple of problems

  1. Sep 8, 2013 #1
    1. The problem statement, all variables and given/known data
    At a time 0.22 seconds after it has been hit by a tennis racket, a tennis ball is located at (6, 8, 0)  m, relative to an origin in one corner of a tennis court. At a time 0.26 seconds after being hit, the ball is located at (6.52, 8.16, 5.88)  m. Calculate the following results, and include correct units:

    (b) What is the average speed of the tennis ball?

    2. Relevant equations

    3. The attempt at a solution

    I had to calculate the average velocity. I got (13, 4, -3) m/s and I have the unit vector (.934, .287, -.215). i know that vavg = deltad/deltat. The problem is that the speed is a scalar and that confuses me.
  2. jcsd
  3. Sep 8, 2013 #2


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    Speed = Distance/Time.

    You are given the time. Calculate the distance between the two points.
  4. Sep 8, 2013 #3
    Given such a short time interval we can safely approximate the path of the ball to straight line by ignoring the effect of gravity. For a particle moving in a straight line which doesn't change its direction of motion the magnitude of the average velocity vector gives the average speed.
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