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Homework Help: Torque/Rotational Dynamics HW Problem

  1. Dec 5, 2011 #1
    1. The problem statement, all variables and given/known data

    A uniform thin rod of weight W = 100 N is supported horizontally by two vertical
    props at its ends. At time t = 0 one of the these supports is kicked out. Find the
    force on the other support immediately thereafter.

    2. Relevant equations

    Sum of forces??

    3. The attempt at a solution

    I really don't understand how to even approach this problem. My guess is that its 50 N because each support holds half of the rod. Any help would be greatly appreciated !!
  2. jcsd
  3. Dec 5, 2011 #2
    Ok , I have a new guess now lol... 100N, since it is the only remaining force acting in the + y direction
  4. Dec 5, 2011 #3


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    Homework Helper

    I think your first guess was right, but I don't know how to solve this one.
    I think it is a rotational motion question. It will rotate about the supported end. You can calculate the torque about that pivot and then find the angular acceleration. That is pretty much a complete description of the initial motion. What if you figure out from the rotational motion how the center of mass accelerates down and say it should fall the same way using F = ma where F is the total of the pivot force and the mg force?
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