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Homework Help: Statics: Equilibrium

  1. Feb 13, 2010 #1
    I have having trouble solving this statics problem, I sum up the forces and have

    C*cos(30) - B*cos(phi) = 0 in the positive x direction
    C*sin(30) + B*sin(phi) - D =0 in the positive y direction

    B = 275 lbs and D = 300lbs
    I need to solve for C and phi, I have tried substitution, division, not matrices because it wouldn't work
  2. jcsd
  3. Feb 13, 2010 #2


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    C*cos(30) = B*cos(phi).........(1)
    C*sin(30) = - B*sin(phi) + D ....(2)
    Divide (2) by (1).You get
    tan(30) = B*cosφ/(B*sinφ - D)
    Square both the sides. Write cos^2(φ) = 1 - sin^2(φ) and solve the quadratics to find φ.
  4. Feb 13, 2010 #3
    Thanks for the reply,

    I divided (2) by (1) but I have

    Tan(30) = (-B*sin(φ) + D)/ (B*cos(φ))

    Am I missing something?
  5. Feb 13, 2010 #4


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    Now square both sides. And simplify.
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