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: Tension in ropes problem

  1. Dec 20, 2004 #1

    I'm having trouble with this problem...I need to figure out the tension in the top rope (the horizontal one). The diagonal bar is 7.5m long and weighs 8kg, and the thing that's supposed to be a stoplight is 12kg.

    So far, I have to figure out the vertical and horizontal components of the hinge (A) and the tension of the rope. I've figured out 2 of the three equations, the ones for forces in the X and in the Y. I can't figure out the torque ones though...Assuming that we choose point A as the pivot point, what's the equation? I know you have a torque coming from the bar, (3.75*8kg*g), a torque from the stoplight (12kg*7.5m*9.8), but I don't what's countering that. The answers are: tension = 2.5 x 10^2, horizontal is 2.5 x 10^2, and verticle is 2.0 x 10^2.
    Last edited by a moderator: Apr 21, 2017
  2. jcsd
  3. Dec 20, 2004 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Okay, write down the equations you've got so far. One of them should tell you the vertical component of the reaction at the hinge.

    As for the torque : what's countering it is the torque from the tension in the rope = T*3.8.

    From this, you can find T.

    With this value of T and the X-equation, you get the horizontal component.
    Last edited: Dec 20, 2004
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook