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!

Suspended Sign

  1. Sep 28, 2009 #1
    1. The problem statement, all variables and given/known data

    Attached is a diagram of the problem.

    A 28kg sign is suspended by two massless cables. Find the tension in each.

    2. Relevant equations

    3. The attempt at a solution

    I'll call the cable at 57 degrees T1 and the other cable T2.

    T1∙cos 57 + T2∙cos 36 = 9.8m/s2∙28kg
    T1∙cos 57 + T2∙cos 36 = 274.4N

    T1∙sin 57 + T2∙sin 36 = 0N

    This is where I'm getting confused - rusty on my algebra with simultaneous equations. Am I on track so far though, then just solve for T1 and T2?

    Attached Files:

  2. jcsd
  3. Sep 29, 2009 #2
    T1 = (-T2∙sin 36)/sin 57

    Substitute that into the first equation...

    (-T2∙sin 36∙cos 57)/sin 57 + T2∙cos 36 = 274.4N
    T2 = 143.05N

    Then solve for T1.

    T1∙cos 57 + (143.05N)∙cos 36 = 274.4N
    T1 = 291.33N
  4. Sep 29, 2009 #3


    User Avatar
    Homework Helper

    From third equation you can write
    T1 = - T2*sin36/sin57.
    Substitute this value in eq. 2 and solve for T2.
  5. Sep 29, 2009 #4
    Thanks - that's exactly what I ended up doing. Not sure why I was over-complicating it. Could anyone confirm my solutions are correct?

  6. Sep 29, 2009 #5
    Can anyone verify that my work is correct? Thanks!
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook