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Homework Help: Boxes, cables, and girders (torque and equilibirum problem)

  1. Sep 26, 2009 #1
    Usually I'm pretty good with torque and such but this one had me.
    A box of mass 75 kg is put on a 10-m long steel beam of mass 150 kg and is connected to the wall and supported by a steel cable. The box is located 2.5 m from the wall and the cable makes 60o angle with the beam. What are the magnitude and the direction of the force exerted by the wall on the beam?

    2. Relevant equations
    Torque=Radius x Force, upwards/clockwise torque=downwards/counterclockwise torque, weight=mass x gravity

    3. The attempt at a solution
    I was able to find the tension in the cable, if that helps (14321.475N), but otherwise I'm clueless.
  2. jcsd
  3. Sep 26, 2009 #2


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    Homework Helper

    Kind of odd using a 10 m long beam to support a box only 2.5 m away from the wall. Or have I misunderstood?

    The usual approach is to write that the sum of the moments about a point (in this case the point where the beam attaches to the wall) is zero. I can't go much further until you give it a try and show your work here.
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