Moment of Inertia of L-shaped bar

  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
    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. Doc Al

    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. 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. Doc Al

    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. I'll scan in the picture tomorrow along with the question
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