1. Not finding help here? Sign up for a free 30min 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!

What force do ropes exert on a sign

  1. Nov 21, 2008 #1
    1. The problem statement, all variables and given/known data
    A sign that weights 648 N is suspended by two ropes that make an angle of 38o with the horizontal. What force does each rope exert on the sign?


    2. Relevant equations
    A + B + W= 0
    Fh= F cos x
    Fv= F sin x


    3. The attempt at a solution
    This is how my textbook says to do it:

    The direction of W is down, so the direction of A + B is up. The sum A+B has no horizontal components, so the horizontal components of A and B, Ah and Bh have equal magnitudes. Now, Ah = Acos38o and Bh=Bcos38o. Since Ah=Bh, the magnitudes of A and B must be equal. The magnitude of the sum of the vertical components of A and B equals the magnitude of the weight of the sign, 648 N. That is, Av + Bv =648 N Since Av = Asin38 and Bv = Bsin38 and A=B, Av=Bv.
    Thus,
    Av=Bv =1/2(648N)= 324N
    And.. A=Av/sin38 = x
    B=A= x

    They don't tell me what x should be, nor what the 324N is for. Please help
     
  2. jcsd
  3. Nov 21, 2008 #2

    stewartcs

    User Avatar
    Science Advisor

    Start by drawing a free body diagram (FBD). Then uses Newton's second law (Fnet = ma) in both the x and y directions. You'll end up with two equations that you can solve simultaneously.

    HINT: The force that the ropes exert on the sign is equal to the tension in the ropes.

    CS
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?