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Homework Help: Speed of a Pendulum

  1. Nov 24, 2008 #1
    1. The problem statement, all variables and given/known data
    A 2.0 M long pendulum released from rest with the support string at an angle of 25 degrees with the vertical. What is the speed of the bob at the bottom of the string?

    2. Relevant equations
    PE = mgy
    KE = 1/2mv^2
    Trig functions

    3. The attempt at a solution

    I just need help getting the problem started, in the potential energy formula, we have two unknowns(unless the 2.0 m has to do with the location of the bob, but i am not certain).

    Thanks in advance :]
  2. jcsd
  3. Nov 24, 2008 #2
    Yes, the 2.0m has something to do with the location of the bob. Use the bottom of the pendulum's course (2.0 m) as the reference point (at this point the PE is 0 and the KE is at a maximum).

    Ill give you a shove in the right direction. Let's say the height of the bob at it's location at 25 degrees to the vertical is 2.0 - (2.0)cos25.

    Hope this helps.
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