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Homework Help: Hanging Beam

  1. Mar 19, 2012 #1
    1. The problem statement, all variables and given/known data

    A purple beam is hinged to a wall to hold up a blue sign. The beam has a mass of mb = 6.7 kg and the sign has a mass of ms = 16.8 kg. The length of the beam is L = 2.43 m. The sign is attached at the very end of the beam, but the horizontal wire holding up the beam is attached 2/3 of the way to the end of the beam. The angle the wire makes with the beam is θ = 32.9°.

    Q1: What is the net force the hinge exerts on the beam?
    Q2:The maximum tension the wire can have without breaking is T = 921 N.
    What is the maximum mass sign that can be hung from the beam?

    2. Relevant equations

    τ=0 as it is static
    F=0 as it is not moving

    3. The attempt at a solution

    For the first question, I form τ=0 where I have 3 torque, τ of tension, τ of beam and do I include τ of the sign?
    And sum of forces is 0, so I have forces on hinge of x is Fh,x-Tcosθ=0, component of y is Fh,y-mbg-msg-Tsinθ=0
    mbg is mass of beam, msg is mass of the sign.
    Is there somewhere I did it wrong?

    Second question I use r*T=(mb*horizontal distance from the hinge+m*horizontal distance from the hinge)*9.81
    Is this correct?
    Last edited: Mar 19, 2012
  2. jcsd
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