1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    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!

Objects in equilibrium hinged platform with cable problem

  1. Apr 13, 2014 #1
    1. The problem statement, all variables and given/known data
    A hinged platform flagpole weighing 500 newtons is supported in the horizontal position by a cable as shown in figure 4.35 db4208af-4577-4e0c-9851-aba4c6f18afb.jpe . Find the tension in the cable and the horizontal and vertical forces at the hinge. Angle ø = 30°

    2. Relevant equations
    T= F* the lever arm

    3. The attempt at a solution
    What I did was created the three equations R cos θ -T cos 30=0 for the X forces
    where R is the resultant force of the wall acting on the hinge of the beam and T is the tension in the wire. The equation for the Y forces was R sin θ + T sin θ -500=0. Then I made the equation T sin 30 (x) -500 (1/2)(x)=0 for the sum of the torques is zero. My problem is I have four unknowns and only three equations meaning I can't substitute. What do I do now? The correct answer is T = 500 N and Rx= 433 N Ry= 250 N
    Last edited: Apr 13, 2014
  2. jcsd
  3. Apr 14, 2014 #2
    Maybe just go ahead and solve for R and T in terms of x and theta and see what happens.
  4. Apr 14, 2014 #3
    I don't think that will work because you have more unknowns than you have equations to work with. I tried it and it doesn't seem to work.
  5. Apr 14, 2014 #4
    if you did it correctly then I think you would see that one of those variables actually drops out
  6. Apr 14, 2014 #5
    Ok I see it now thanks!
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted