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Homework Help: Simple Moment of Inertia Question

  1. Jan 2, 2009 #1
    1. The problem statement, all variables and given/known data
    A rod of negligible mass is pivoted about one end. Masses can be attached to the rod at various positions along the rod. Currently, there is a mass (m) attached a distance (L) from the pivot. To increase the moment of inertia about the pivot by a factor of 5, you must attach...

    2. Relevant equations


    3. The attempt at a solution

    Io= mL^2
    If= 5(Io) = mL^2(original mass)+4(mL^20) All I did was add four more masses of equal size at a distance L from the pivot. Is there another solution?
  2. jcsd
  3. Jan 3, 2009 #2


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    Gold Member

    You are correct. The definition of moment of Inertia is [tex]\sum_{i} m_{i} r^{2}_{i}[/tex]
  4. Jan 3, 2009 #3

    Doc Al

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    Staff: Mentor

    Sure, there are plenty of solutions. The question is a bit vague. Are there any constraints given? (Such as the the number of masses you are allowed to add or the size of the masses.)

    For example: What if you could only add a single mass of equal size. How could you solve the problem then?
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