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Equilibrium of a particle - hibbeler , help please

  1. Nov 3, 2007 #1
    [SOLVED] Equilibrium of a particle - hibbeler , help please

    Hi all
    I was surfing the net looking for a physic / mechanic forum and thank god i found this.
    I have problem with solving Equilibrium problems, hopefully you guys and girls would help me out.

    1) Question. ( this is problem 3-1 , in engineering mechanic statics , 11th edition hibbeler)

    - Determine the magnitudes of F1 and F2 so that the particle is in equilibrium
    Given : F1 = 500N , θ1 = 45deg and θ2 = 30 deg

    2) this is how far i went.

    ΣFx = F1 cos θ1 + F2 cos θ2 - F = 0

    ΣFy = F1 sin θ1 -F2 sin θ2 = 0
    -
    ΣFx = F1 cos 45 + F2 cos 30 - 500 = 0

    ΣFy = F1 sin 45 -F2 sin 30 = 0 -> f1sin 45 = f2sin 30

    so , f1 cos 45 + f1sin 45 - 500 = 0
    f1 cos 45 + f1 sin 45 = 500
    f1 1.41 = 500
    500 / 1.41 = 354.60

    well that answer is wrong , i know that f1 = 259 and f2 = 366 those are the correct answers

    any help guys
    thanks in advance
     
  2. jcsd
  3. Nov 3, 2007 #2

    PhanthomJay

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    Science Advisor
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    Gold Member

    You need to be a bit more specific in the problem statement.... are there 3 forces F1, f1, and f2? Direction of F1?? theta reference axis?? etc.
     
  4. Nov 3, 2007 #3

    Astronuc

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    Staff: Mentor

    This so
    is not consistent with
    Taking ΣFx = F1 cos θ1 + F2 cos θ2 - F = 0, and θ1 = 45° and θ2 = 30°, then

    F1 cos (45°) + F2 cos (30°) = 0.7071 F1 + 0.866 F2 = 500 N.

    The other equation is F1 sin 45° -F2 sin 30° = 0 = 0.7071 F1 - 0.5 F2 = 0.

    Subtract the first equation from the second and one obtains

    1.366 F2 = 500 N

    Solve for F2 and substitute that value into either equation and solve for F1.
     
  5. Nov 3, 2007 #4
    Thank you very much for your help.
     
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