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Homework Help: Ball Energy question

  1. Oct 29, 2008 #1
    1. The problem statement, all variables and given/known data

    Hey guys.
    Look at this problem.
    This is the question in short, they release a ball with mass m and radius r from 2R high into a loop. the balls movement is without sliding.
    The first part of the question is to find the angle (alpha) in which the ball disconnects from the surface, I did that.
    The second part, is to find H which is the maximum high that the ball will reach to (as you can see in the sketch).
    In there solution, they used energy conservation (the equation I marked in red). My problem with that equation is, that when the ball reaches max high, it still has velocity on the x axis and they just ignored it.
    So, my question is, is that equation right? am I missing something?
    thanks.

    2. Relevant equations



    3. The attempt at a solution
     

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