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: Static Equilibrium Weight Problem

  1. Nov 16, 2009 #1
    The mass of the sign shown is 28.5 kg. Find the weight supported by (a) the left support and (b) the right support.

    How do I set this problem up properly?

    Here is my set up even though I know its wrong.

    m = 28.5kg, mg = 279.3N

    Fl + Fr = mg

    Fl = mg - Fr

    t = torque, r = radius

    tl + tr = mg

    Fl*rl + Fr*rr = mg

    (mg - Fr)*rl + Fr*rr = mg

    mg*rl - Fr*rl + Fr*rr = mg

    then I plug in the radius of the right and left posts using 1.2m for the left post and .3m for the right post, and 279.3 for mg and solve.

    How do I properly set this problem up?

    Attached Files:

  2. jcsd
  3. Nov 16, 2009 #2


    User Avatar
    Homework Helper

    Weight of the sign board act at the center of the board in the downward direction.
    When you write Fl + Fr = mg, Fl and Fr are in the upward direction.
    To find the torque, select a reference point, say left end of the sign board.
    Then find the torques due to Fl, Fr and mg. Which one is CW and which one is CCW?
    Equate them to find Fr. Then proceed further.
  4. Nov 16, 2009 #3
    ah ok, I see it now. I didnt account for the torque of the sign itself.

    thank you!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook