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Statics - 3 forces acting at a point -- angle α maxima

  1. Aug 2, 2015 #1

    SFG

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    1. The problem statement, all variables and given/known data

    Please if anyone could help me with this question .

    Two wires AC and BC are attached to the top of pole CD . The force exerted by the pole at C is vertical and the 2.5 kN force applied at C is horizontal and makes an angle α with the direction of the x-axis .

    Find the angle α for which the tension in AC is a maximum and the corresponding tension in each cable .

    as per pdf diagram

    2. Relevant equations

    Cos ^2 ɸx + Cos ^2 ɸy + Cos ^2 ɸz = 1

    F = √Fx^2 + Fy^2 + Fz^2

    Cos ɸz = Fz/F



    3. The attempt at a solution


    Formulate a quadratic then differentiate to get a maxima .

    Sorry I cannot find the start point for this solution . Please help
     

    Attached Files:

  2. jcsd
  3. Aug 2, 2015 #2
    Try summing forces in the x-direction.
     
  4. Aug 2, 2015 #3

    mfb

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    2016 Award

    Staff: Mentor

    Which force balances do you see that you can set up?
     
  5. Aug 2, 2015 #4

    SFG

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    guys I am looking . seriously I am blanked without knowing another force or vector locations . regards SFG
     
  6. Aug 2, 2015 #5

    mfb

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    Staff: Mentor

    The top of the pole is the only thing that can move, so it is useful to look at forces acting on that.
    If you do not know a quantity, introduce a variable for it. That is something you will have to do frequently and everywhere.
     
  7. Aug 2, 2015 #6

    SFG

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    ok thanks guys . i'll work on this overnight . regards
     
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