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Homework Help: Simple Pendulum - Maximum Speed

  1. Apr 13, 2010 #1
    1. The problem statement, all variables and given/known data:

    A simple pendulum has a mass of 0.25 kg and a length of 1.0 m. It is displaced through an angle of 5.0° and then released.

    1. What is the maximum speed?

    2. What is the maximum angular acceleration?
    Answer: 0.855 rad/s2

    3. What is the maximum restoring force?
    Answer: 0.214 N


    2. The attempt at a solution:

    I got numbers 2 and 3 right, but I can't figure out number 1.

    Here's my attempt:

    m*g*L*sin [tex]\theta[/tex] = 1/2 *m*v2
    (0.250)*(9.81)*(1.0)*(sin 5) = 1/2 * (0.250)*v2
    0.124 = (0.125)v2
    v2 = 1.712 = 1.31 m/s

    It is incorrect. Can someone please help me as to where I went wrong?
     
    Last edited: Apr 13, 2010
  2. jcsd
  3. Apr 13, 2010 #2

    rock.freak667

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    Homework Helper

    You are equating a force to energy.

    First draw a free body diagram and find the potential energy when it is displaced at 5°.
     
  4. Apr 13, 2010 #3
    I drew the diagram, but I'm not sure how to find the potential energy?
     
  5. Apr 14, 2010 #4

    rock.freak667

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    From the lowest point to where it is displaced, what is the vertical height?
     
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