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Homework Help: Torque and forces.

  1. Apr 28, 2008 #1
    1. The problem statement, all variables and given/known data
    Two balls are connected together and fall through air. They also rotate around the center of mass. I'm supposed to find an equation for the torque of air resistance through the center of mass.
    Fk= Force due to air resistance on each of the balls
    w=angular velocity
    Vcm=velocity of the center of mass
    M=mass of each ball
    R=radius of each ball
    Icm=moment of inertia in the center of the mass
    Ia=Ib= moment of inertia for each ball
    r= position of the ball relative to the center of mass

    2. Relevant equations
    Va=Vcm+w X r
    Vb=Vcm - w X r
    This is the answer I'm supposed to get: T=-2Kv*w*R^2

    3. The attempt at a solution
    I have tried sooo many different ways to get this.
    And still I have no idea. Can anyone help me?
  2. jcsd
  3. Apr 28, 2008 #2


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    Staff Emeritus
    Science Advisor
    Gold Member

    Hi mathildej and welcome to PF,

    Would you mind detailing some of the methods you have tried?
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