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Homework Help: Moment of Inertia Questions

  1. Oct 8, 2004 #1
    **The problem and solution is attached as moment of inertia.**
    **The equations for moment of inertia of known homogeneous solids is also attached**

    I'm having some trouble grasping this concept. I hope someone can help clarify some things for me.

    Looking at the problem I realized I would have to use the parallel axis theorem, but after that the trouble begins. (I = Ig + m*d^2)

    "Deterimine the wheel's M of I about an axis perpendicular to the page and passing thru pt A."

    What does this mean? What is it saying?

    And a related question to the above: Why when calculating M of I for the thin ring (Homogeneous solids jpeg) do you use Izz = m*r^2 instead of Ixx or Iyy? Same question for the slender rod. How do you know which one to use?

    I realize I've said a lot, but I hope someone can give me some pointers.

    Attached Files:

  2. jcsd
  3. Oct 8, 2004 #2
    Have you identified what the axis passing through A looks like?

    The axis A appears parallel to the z axis judging from the orientation of the second picture so yes you are correct. If you look at the orienation of the rods they are perpendicular to the A axis so judging from the second picture again you should use the y M of I.

    My personal opinion is that for simple objects like that it is easier to derive the M of I so perhaps just remembering that the M of I is in integral form (r^2dm)
    Last edited by a moderator: Oct 8, 2004
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