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Simple Moment of Inertia question

  1. Dec 6, 2006 #1
    Rotating a massless rod of length R about the midpoint of the rod with a mass of 2m attached to one end and a mass of m to the other. What is the moment of inertia?

    My book is terrible at giving good examples, there's nothing similar to this.

    Do I treat them as two seperate point particles, take the moment of inertia of each around the axis and add them? (2m*(r/2)^2) + (m*(r/2)^2) I'm assuming I can treat them as points, the drawing has the masses as clearly different sized spheres, but says nothing about their radius or anything of that nature.

    Thanks in advance guys.
  2. jcsd
  3. Dec 6, 2006 #2
    I think I have it right, would still appreciate confirmation though, thanks guys.
    Last edited: Dec 6, 2006
  4. Dec 7, 2006 #3
    Your concept is correct, but I think you meant diameter instead of radius for the term r used in your equation.
  5. Dec 7, 2006 #4
    Actually the book used R as the length of the rod, I probably shouldn't have used lower case there, sorry about the confusion. Thanks again.
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