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Homework Help: Farmyard Gate - Equillibrium

  1. Apr 13, 2008 #1
    1. The problem statement, all variables and given/known data
    A gate 4.00 m wide and 2.00 m high weighs 528 N. Its center of gravity is at its center, and it is hinged at A and B. To relieve the strain on the top hinge, a wire CD is connected to the gate at an angle of 30 degrees. The tension in CD is increased until the horizontal force at hinge A is zero. What is the tension in wire CD?


    2. Relevant equations
    ΣF=0
    Στ=0
    τ=r*F


    3. The attempt at a solution

    Fx=Tension(cos(30))
    Fy + Tension(sin(30))=528
    Tension(sin30)(4m)=528(2m)
    Tension= 528N
    This is very wrong, I am so lost and confused please help.
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Apr 14, 2008 #2
    where relative to the center are the hinges and the wire located?
     
  4. Apr 14, 2008 #3

    tiny-tim

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    Science Advisor
    Homework Helper

    Hi kontroll2007! :smile:

    Hint: if the horizontal force at A is zero, then that means the total force at A is vertical.

    So if you take moments about any point on the vertical line through A, the contribution from A will be zero.

    Does that help? :smile:

    (erm … we can't help you any more until you tell us where C and D are … they're obviously not the other two corners of the gate! :redface:)
     
  5. Apr 14, 2008 #4
    Sorry, but they would not let me put a link to the picture in the post. Ok D is above A on a post while C is on the side opposite the hinges.
    |D
    |
    A |{---------- C
    || |
    B |{----------
     
  6. Apr 14, 2008 #5

    tiny-tim

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    Science Advisor
    Homework Helper

    ok … so which point on the line DAB should you take moments about to find the tension when the force at A is vertical? :smile:
     
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