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Farm Gate Problem

  1. Mar 18, 2009 #1
    Old MacDonald had a farm, e i , e i , oh ! And
    on that farm he had a gate, e i , e i , oh ! And
    a squeak, squeak, here. A squeak, squeak,
    there. And a squeak, squeak, everywhere . . .
    The gate is ℓ = 3 m wide and h = 2.47 m
    tall with hinges attached to the top and bot-
    tom. The guide wire makes an angle of
    α = 39 ◦ with the top of the gate and has
    a tension of 221 N. The mass of the gate is
    30.9 kg.

    Determine the magnitude of the horizon-
    tal force exerted on the gate by the bottom
    hinge. The acceleration of gravity is 9.8 m/s2 .
    Answer in units of N.

    Okay the reason why I am having problems with this is because well im just not sure I know where to start. I think I am just missing something obvious, and my book does not have a whole lot to say about this type of problem. Any Help?
     
  2. jcsd
  3. Mar 19, 2009 #2

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    Hi xRandomx210! :smile:

    (ooh, that gate is really annoying :frown: … if i help with the question, will you please oil it?)

    There are only four external forces on the gate.

    You know 2 of them, and you want one of them, but you don't know the fourth one, and and you don't want to know it, so … standard trick … take moments about the point of application of that unknown force. :wink:
     
  4. Mar 19, 2009 #3
    Sorry for being a noob, but what does oiling it mean?
     
  5. Mar 19, 2009 #4
    Just tried something, dont know if it is right or not.

    Σfx= TCos(Theta) = H1x+H2x

    where Hx is the force of the hinge in the x direction

    Σfy=TSin(theta) + Hy1 + Hy2 = mg

    ΣT = mg(L/2)-Tsin(theta)L= Hx(h)

    from there you can slove out, but is the method correct?
     
  6. Mar 19, 2009 #5
    Never mind the reason i got it wrong the first time was because i used 9.81 instead of 9.8 :C
     
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