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Homework Help: Moment Of Inertia Of A Semi-Circular Disk?

  1. Apr 26, 2012 #1
    1. The problem statement, all variables and given/known data

    http://dl.dropbox.com/u/630750/Screen%20Shot%202012-04-26%20at%2010.03.36.png [Broken]

    2. Relevant equations

    3. The attempt at a solution

    http://dl.dropbox.com/u/630750/Photo%2026-04-2012%2010%2001%2034.jpg [Broken]

    I know this is wrong but I can't really see why, can anybody help?

    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Apr 26, 2012 #2


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    Hi Roomie! :smile:

    (please type your answers in future)

    Why 1/4 Mr2 ? :confused:
  4. Apr 26, 2012 #3

    Filip Larsen

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    Gold Member

    Your approach is correct, but you've made two mistakes inserting the numbers (hint: you're missing a square and use wrong mass). Check your result again (actually, you should probably make a habit of doing this before posting in the first place)
  5. Apr 26, 2012 #4
    Ah yes I see that I missed a squared, and that makes my answer 0.111. But I don't see how I have used the wrong mass? The mass of the semi circular disk is 10kg?
  6. Apr 26, 2012 #5

    Filip Larsen

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    Gold Member

    Sorry, I misread the text as if the mass of the full disc was 10 kg.

    Reading it correctly I can then only ask as tiny-tim did (that is, check your equation for the moment of inertia around O).
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