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Homework Help: Moment of Inertia + Energy question

  1. Nov 3, 2007 #1
    1. The problem statement, all variables and given/known data
    A uniform rod of mass 3 kg is 17 m long. The rod is pivoted about a horizontal, frictionless pin at the end of a thin extension (of negligible mass) a distance 17 m from the center of mass of the rod. Initially the rod makes an angle of 66◦ with the horizontal. The rod is released from rest at an angle of 66◦ with the horizontal, as shown in the figure below The acceleration of gravity is 9.8 m/s2.
    Hint: The moment of inertia of the rod about its center-of-mass is Icm = 1/12mL^2.

    What is the angular speed of the rod at the instant the rod is in a horizontal position?
    Answer in units of rad/s.

    2. Relevant equations

    3. The attempt at a solution
    The moment of inertia I got for the whole system was:
    I've managed to get:
    w=[tex]\sqrt{\frac{6gh}{L^2}}}[/tex], with w being the angular speed
    But I am unsure if h is L*sin(theta) or (3/2L)*sin(theta), since the rod is off the pivot.

    Any ideas?
  2. jcsd
  3. Nov 4, 2007 #2
    Here's the figure that went along with it:

    http://img103.imageshack.us/img103/9987/hw10q1ex1.jpg [Broken]
    Last edited by a moderator: May 3, 2017
  4. Nov 4, 2007 #3
  5. Nov 4, 2007 #4
    I still don't know.
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