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Homework Help: Moments of Inertia

  1. Apr 10, 2007 #1
    So I have a point A on a graph with x and y axes. From the origin, the point is 3r to the right, and 1r up. I'm to find the Moment of Inertia along the x, y, and z axes. I've found the x and y moments, but not the z and I'm not really sure on how. I'm not getting any ideas from the graph alone. How do I start?
  2. jcsd
  3. Apr 10, 2007 #2
    Bump, anybody?
  4. Apr 11, 2007 #3


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    Homework Helper

    The z-axis points up out of the page. The moment of inertia of the point mass about the z-axis will be

    [tex]I_z = md^2[/tex]

    where d is the shortest distance of the point mass from the z-axis. Since the point mass is on the x-y plane d will be the distance that the point mass is from the origin. That is it is the hypotenuse of the right triangle formed by its x and y- components.
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