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Homework Help: Extended free body diagram

  1. Oct 31, 2011 #1
    1. The problem statement, all variables and given/known data
    I need help with this: http://img716.imageshack.us/img716/3262/unledewk.jpg [Broken]

    I know that I need to create an extended free body diagram and I understand how to get all the equations from the diagram. BUT I don't know what to do when it comes time to use torque and find tension

    2. Relevant equations
    T = Ialpha

    3. The attempt at a solution
    x-component : N - Tcos(35) = 0
    y-component : Tsin(35) + U - 2.5g = 0

    I get stuck at this point and don't know how to use torque to solve for T. I'm pretty confused with the concept of it, so if you can, please try to be a little thorough in walking me through the rest of the problem.
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Oct 31, 2011 #2
    There are 3 unknown physical quantities and so we require 3 equations if one wants to find all three unknowns.

    The third equation is the torque equation as you yourself mentioned. I would take moments about the pin so that forces U and N do not enter.

    Remember that moment of a force about a point is given by the product of the force and perpendicular distance of the line of action of this force from the given point.

    One can simplify the moment equation if the tension is resolved into components - one along the bar and passing through the pin and the other perpendicular to the bar.
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