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Homework Help: Can somone explain this review solution (moments/inertia)?

  1. May 4, 2017 #1
    1. The problem statement, all variables and given/known data
    Capture.PNG

    2. Relevant equations
    This would be the part I think I'm missing

    3. The attempt at a solution
    In the fourth line, Ix, where is the justification for multiplying 1/3 by the first term? I believe they are using the center of inertia of a rod, which is mr2 and the first term doesn't make much sense. Could someone explain to me the justification of that line?
     
  2. jcsd
  3. May 4, 2017 #2

    haruspex

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    There seems to be some confusion over the axes. They must mean Iy.
    The part that matters is just the three sides of length 0.2m. Two of them are rotating about one endpoint, hence the 1/3 and the factor 2 at the front. The middle bar is parallel to the axis, so just mr2 for that piece.
     
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