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Homework Help: Forces on bar

  1. Dec 3, 2007 #1
    1. The problem statement, all variables and given/known data
    The 2 kg rod AB and the 3kg rod BC are connected as shown to a disk that is made to rotate in a vertical plane at a constant angular velocity of 6 rad/s clockwise. For the position shown, determine the forces exerted at A and B on rod AB.

    2. Relevant equations
    summation of forces
    mass moment of inertia
    relative velocites and accelerations

    3. The attempt at a solution
    I think I solved the accelerations and angular accelerations correctly but at this point I'm unclear as to what to do next.
  2. jcsd
  3. Dec 3, 2007 #2


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    Staff Emeritus
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    Gold Member

    Looks good so far!

    You accidentally set the wrong component to zero in the line for a_A, but you fixed it in the next line. Make sure you correct that line too!

    Now that you have a_A and a_B, throw away everything except rod AB. You can now describe the dynamics of rod AB in terms of a center of mass acceleration (=(a_A+a_B)/2) and an angular acceleration about the center (=(a_A-a_B)/L). This can be seen as coming from a pure force (acting at the center) and a pure couple (torque about the center). From here, finding the forces at A and B is just a matter of adding and subtracting.
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