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Homework Help: Pendulum question

  1. Mar 22, 2010 #1
    1. The problem statement, all variables and given/known data

    A simple pendulum, 2.0 m in length, is released from rest when the support string is
    at an angle of 25° from the vertical. What is the speed of the suspended mass at the
    bottom of the swing?

    2. Relevant equations

    R2= X2 + Y2

    3. The attempt at a solution

    I know the answer is 1.9ms-1

    but i keep getting 1.8126ms-1

    which is 2.cos(25)
    what am i doing wrong?
  2. jcsd
  3. Mar 22, 2010 #2
    If you are going to use conservation of energy, for example, then you equate the k.e. at the lowest point to the p.e. at the highest.
    The mass has risen a vertical height 2 - 2.cos25. when moved to its starting point.
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