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3-D equilibrium

  1. Sep 20, 2009 #1
    1. Collars A & B are connected by a 525-mm long wire and can slide freely on frictionless rods. If force P= (341 N)j is applied to collar A determine the tension of the wire when y=155mm and the magnitude of force Q(which is along the z axis) to maintain equilibrium

    2. Relevant equations
    [tex]\Sigma[/tex]F=0

    [tex]\overline{v}[/tex]=[tex]\sqrt{vx^2+vy^2+vz^2}[/tex]

    3. The attempt at a solution

    I was given y was 155mm and x=200mm and found the z value of the wire to be 460mm. I then created a unit vector for the wire and came up with these equilibrium formulas:

    [tex]\Sigma[/tex]Fx=[tex]200/525[/tex]Tab=0 (Something is wrong here)

    [tex]\Sigma[/tex]Fy=[tex]-155/525[/tex]Tab=-341N

    [tex]\Sigma[/tex]Fz=Q+[tex]460/525[/tex]Tab=0

    Now I'm stuck....can anyone lead me in the right direction?
     
  2. jcsd
  3. Sep 21, 2015 #2
    Think about Newton's 3rd Law of Motion - action and reaction. So you know that a force P acting on point A will make it move up and also create tension on T(ab). However, you know also that T(ab) must have three components of xyz. The problem is that point A can only move at y axis, but to satisfy equilibrium, there must be a hidden force opposite of T(ab) in which it will make the sum of the forces on x and z zero.
     
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