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Homework Help: Problem Understanding Physical Pendulum

  1. Sep 26, 2007 #1
    I am having trouble understanding what h is in the equation for T listed below. Here is an image th_Photo1.jpg


    The Problem: A physical pendulum consists of a uniform circular disk (of R=2.35cm) supported in a vertical plane by a pivot located a distance D=1.75cm from the center of the disk. The disk is displaced by a small angle and released. What is the period T of the resulting SHM?

    Equations:
    [tex]T=2\pi\sqrt{\frac{I}{mgh}}[/tex]

    [tex]I=I_{cm}+mH^2[/tex]

    from text [tex]I_{disk}=\frac{1}{2}MR^2[/tex]

    This is where I am messing up either my algebra or what I am interpreting as h.

    For the parellel-axis theorem I had [tex]I_{disk}=\frac{MR^2}{2}+MD^2[/tex] where D is the distance from the COM to the pivot.

    and for h in mgh I thought the total height was h=D+R.

    Am I correct about what h is? Or no? This will determine what my mistake is:yuck:

    Thanks
    Casey
     
    Last edited: Sep 26, 2007
  2. jcsd
  3. Sep 26, 2007 #2
    Don't worry...I got it.
     
    Last edited: Sep 26, 2007
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