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Rotational Momentum Problem

  1. Jul 14, 2009 #1
    1. The problem statement, all variables and given/known data
    A student sits on a rotating stool holding two 4.0 kg objects. When his arms are extended horizontally, the objects are 1.0 m from the axis of rotation, and he rotates with an angular speed of 0.75 rad/s. The moment of inertia of the student plus stool is 3.0 kg·m2 and is assumed to be constant. The student then pulls the objects horizontally to 0.50 m from the rotation axis.
    (a) Find the new angular speed of the student. rad/s
    (b) Find the kinetic energy of the student system before and after the objects are pulled in.




    2. Relevant equations



    3. The attempt at a solution
    Tried working the problem but got stuck with not having the moment of inertia after the weights are pulled in. All of the examples my proffessor worked in class gave us both so i am unsure how to solve for it.
     
  2. jcsd
  3. Jul 14, 2009 #2

    cepheid

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    Moment of inertia is typically a function of radius, is it not? All that has changed is the radius of the circle being swept out by the two masses.
     
  4. Jul 14, 2009 #3
    B-12:

    Can you calculate the Moment of Inertia for a single point mass a distance 'r' from an axis of rotation?
     
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