1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: 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


    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
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook