Moment of Inertia of L-shaped bar

  1. Dec 1, 2007 #1
    1. The problem statement, all variables and given/known data
    Find the mass moment of inertia of a L-shaped bar that has legs of 1.2 m long and total mass of bar is 20 kg.


    2. Relevant equations
    I=1/12*m*L^2
    parallel axis theorem


    3. The attempt at a solution
    I've tried attempting this problem but I just can't figure out how to apply mass moments to the parallel axis theorem.

    Any help on this problem would be greatly appreciated. I need to figure this mass moment of inertia for a rotational dynamics problem I'm working on.
     
  2. jcsd
  3. Dec 1, 2007 #2

    Doc Al

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    Staff: Mentor

    Add the moment of inertia of each "leg" together to get the total. Where's the axis of rotation?

    The formula you gave is for a thin rod rotating about its center. You can use the parallel axis theorem to find the moment of inertia of a thin rod about any parallel axis.
     
  4. Dec 3, 2007 #3
    still no luck

    I do not know where the axis of rotation is. The problem states that a slender L-shaped bar is at rest in a vertical plane.

    a bar rotating about it's end is 1/3mL^2
     
  5. Dec 3, 2007 #4

    Doc Al

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    Staff: Mentor

    If you're not told the axis, how can you be expected to find the moment of inertia?

    Please post the full problem exactly as given.
     
  6. Dec 4, 2007 #5
    I'll scan in the picture tomorrow along with the question
     
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