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Finding the differential equation for a oscillating system

  1. Dec 8, 2012 #1
    1. The problem statement, all variables and given/known data
    4ABFh.png


    3. The attempt at a solution
    I don't think this is the correct answer because for some reason I have a constant mg term. Usually I get mgsinθ and from small angle approximations it becomes mgθ, but this time I am getting mgcosθ and from small angle approximations it becomes mg.

    9WE42.png

    What am I doing wrong? Or is this correct?
     
  2. jcsd
  3. Dec 8, 2012 #2

    haruspex

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    I don't see the distances in your expressions for the moments.
     
  4. Dec 8, 2012 #3
    I just tried this question and did it with the distances, but I also don't understand why there is a constant term. That term is throwing me off.
     
  5. Dec 8, 2012 #4

    haruspex

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    Please post your working if you'd like further assistance.
     
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