1. Limited time only! Sign up for a free 30min personal 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!

Homework Help: Torque Truss Question

  1. Jan 31, 2006 #1
    Okay, I have uploaded the question to imageshack because it would be to difficult to understand the question without the diagram. Basically, I've done a lot of work on it and know I'm on the right track. If someone could point out where I have made a mechanical error it would be greatly appreciated. The question I am on is number 3.22, the one in the top right corner of the page.

    Go here for picture of question.

    So first off I made a free body diagram. Two Fn's going up, two 150's going down and a 500 going down. I solved for Fn and got 400N.

    Then I solved the triangle to find that the angle between the cord and the board is 54 degrees. Finally I did torque calculations as follows:

    T1 = 400(Fn) * 3 * sin 36
    T1 = -705N

    T2 = T * 2.5 * sin 54
    T2 = 2.02T

    2.02T = 705
    T = 349N?

    The answer should be 280 Newtons. Where have I gone wrong?
  2. jcsd
  3. Jan 31, 2006 #2

    Doc Al

    User Avatar

    Staff: Mentor

    What about the torque due to the weight of the rafters?
  4. Jan 31, 2006 #3
    Damnit. I knew I forgot something.

    Haha thanks bud!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook