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Equilibrium question on review assignment, need help quick (I have a test tomorrow).

  1. Jan 29, 2013 #1
    1. The problem statement, all variables and given/known data
    A rod of negligible mass is supported by a hinge at the wall by a horizontal wire fastened at a 30 degree angle one-third of the way along the rod. A weight of 12 N hangs from the left end of the rod.

    a) Find the tension (T) in the horizontal wire. (T = 62.2 N)
    b) Find the magnitude and direction of the force that the hinge exerts on the end of the rod. (FH = 63 N, 11 degrees NW)


    2. Relevant equations
    Sum of the Torques clockwise = Sum of the torques counterclockwise (ETcw = ETccw)
    Basic trig like sin, cos and tan.



    3. The attempt at a solution
    I solved a) already.
    (Tcos60*1/3d) = (12cos30*d)
    (T*0.1666666) = (10.39230485)
    T= 62.3 N

    (Here is a picture of the diagram; it's not very clear)
    http://twitpic.com/bzeo8w
    The angle the wire makes with the rod is 30 and the angle the weight makes with the rod is 60.
    Question b) however I am completely stuck on, it would be great if someone could explain how to do it step by step.
    http://twitpic.com/bzeo9g
    I tried to find FHy and FHx however nothing made sense to me and I've spent three hours on this.
     
  2. jcsd
  3. Jan 29, 2013 #2

    SammyS

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    Re: Equilibrium question on review assignment, need help quick (I have a test tomorro

    There are only three forces acting on the rod:
    The weight hanging from the end.

    The tension of the wire.

    The force exerted by the hinge.​

    It's a fairly straight forward equilibrium problem .
     
  4. Jan 29, 2013 #3
    Re: Equilibrium question on review assignment, need help quick (I have a test tomorro

    I know but I don't know why the answer is 11 degrees NW, that's where I am confused.
     
  5. Jan 29, 2013 #4

    SammyS

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    Re: Equilibrium question on review assignment, need help quick (I have a test tomorro

    In my opinion, using a compass direction here is rather strange.

    I get the the hinge exerts a force of 63.347 Newtons outward from the wall at an angle of 10.9197° above the horizontal. If that's considered NorthWest, then fine.
     
  6. Jan 29, 2013 #5
    Re: Equilibrium question on review assignment, need help quick (I have a test tomorro

    How do you get 63.347 N for the force that the hinge exerts? Sorry for asking all these questions, this question is just really confusing me though.
     
  7. Jan 30, 2013 #6

    SammyS

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    Re: Equilibrium question on review assignment, need help quick (I have a test tomorro

    [itex]\displaystyle 63.347\approx\sqrt{62.2^2+12^2\,}[/itex]
     
  8. Jan 30, 2013 #7
    Re: Equilibrium question on review assignment, need help quick (I have a test tomorro

    Thank you so much!
     
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