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Homework Help: Conservation of Mechanical Energy Problem

  1. Oct 30, 2004 #1
    A 2.00-kg ball is attached to the bottom end of a length of fishline with a breaking strength of (44.5 N) The top end of line is held stationary. The ball is released from rest with the line taut and horizontal (theta=90.0). At what angle theta(measured from the vertical) will the fishline break.

    I think I have a good idea about this problem, yet I wanted to get someone elses opinion. Taking into account that the potential energy of the ball-earth system is a maximum at the initial position which happens to be at rest. The potential energy changes only when the ball is set into motion which the energy is being transferred to kinetic. If I find the velocity of the ball then I could use this for centripetal acceleration to find the theta in Newton's Second Law. What's throwing me off is determining the length of the string at some point after the ball is released.
  2. jcsd
  3. Oct 30, 2004 #2


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    Consider the string to be, as usual, inextensible, with some length L.
    Since the square of the speed is proportional to L (through energy conservation), the centripetal acceleration will be independent of L.
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