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Moment of inertia, double integral

  1. Apr 14, 2014 #1
    1. The problem statement, all variables and given/known data
    Untitled.png


    2. Relevant equations



    3. The attempt at a solution
    For part B, why is he using the formula for the moment of inertia about the y-axis? Why isn't he using the formula for the moment of inertia about the origin?

    http://www.math24.net/physical-applications-of-double-integrals.html

    The formula that I'm referring to is the "polar moment of inertia" in this list.
     
  2. jcsd
  3. Apr 14, 2014 #2

    maajdl

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    Gold Member

    We can't read any problem statement and relevant equations in you post.
    What's the question?

    Note that a moment of inertia is always defined with respect to an axis (of rotation).
    There is nothing like a moment of inertia about a point like the origin.
     
  4. Apr 14, 2014 #3
    You can't see the picture? I can see it :/.

    The formulas are in the link.
    I don't know what to tell you. The problem is asking for moment of inertia about the origin. The list of integrals also has a formula for "polar moment of inertia".
     
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