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Homework Help: Rotational Inertia Four point masses problem-diagonal

  1. Nov 29, 2011 #1
    Rotational Inertia "Four point masses problem--diagonal"

    1. The problem statement, all variables and given/known data

    Four point masses of 3.0 kg each are arranged in a square on mass-less rod. The length of a side of the square is .50 m. What is the rotational Inertia for rotation about an axis passing through masses A and C?

    A B


    D C




    2. Relevant equations

    I=mr^2


    3. The attempt at a solution

    I have the solution but just don't understand it! I cant on my own find the radius if it's in a diagonal problem like this one. For B and D, the radius is .5m * [itex]\sqrt{}2[/itex] / 2.

    Where does the [itex]\sqrt{}2[/itex] / 2 come from?
     
  2. jcsd
  3. Nov 29, 2011 #2
    Re: Rotational Inertia "Four point masses problem--diagonal"

    Points B and D are each 0.5sin45m away from the axis.OK?
     
  4. Nov 29, 2011 #3
    Re: Rotational Inertia "Four point masses problem--diagonal"

    and sin45 = [itex]\frac{\sqrt{2}}{2}[/itex]
     
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