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Velocity 2D question

  1. Apr 23, 2008 #1
    1. The problem statement, all variables and given/known data

    If a long jumper at the top of his trajectory is moving at 6.5 m/s (horizontally) and his centre of mass is 1.1m abover where it was when he launched into the jump, how fast must he have been moving when he launched?


    2. Relevant equations


    Vx = Vox + ax*t

    3. The attempt at a solution

    In all texts i look at they say that the initial velocity should be the same as final velocity in the x axis but that isnt the correct answer for the question in the text.

    Thanks for any help.
     
  2. jcsd
  3. Apr 23, 2008 #2
    Ask yourself this:

    Is there a force in the horizontal direction that could cause an acceleration or deceleration on the jumper?

    If yes: A force is exerted on the jumper in the horizontal direction thus giving him an acceleration (either forward or backward) thus changing the speed.

    If no: No force is exerted on the jumper in the horizontal direction, so the acceleratoin in the horizontal direction is 0, so the horizontal speed does not change.
     
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