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: Calculating moments of forces/fulcrum PDF file attached

  1. Sep 13, 2011 #1
    1) see pdf
    for question 2 i'm unsure how to calculate the force at the fulcrum since its not in equilibrium. I thought maybe i would add the two forces together, but that doesn't seem right.

    2) so this question asks for what forces need to be applied at points A and B and i understand what forces need to be applied at A ( i think ). but at point B wouldn't the fulcrum have to have an equal amount of force pushing up...so 50+20 = 70N...doesn't seem right since the fulcrum isn't centered.

    please see pdf attached, thanks in advance

    Attached Files:

    Last edited: Sep 13, 2011
  2. jcsd
  3. Sep 14, 2011 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    For question 2
    The statement of the problem is missing, so I assume that the mass of the bar is given. Call it m. You need to write two expressions for Newton's Second Law, ∑F = macm and ∑τ = Ifulcrumα. Here Ifulcrum is the moment of inertia of the bar about the fulcrum.

    For question 3, is there friction at the fulcrum? If no, then it seems that you have put in the right forces. It is assumed that the fulcrum provides whatever force is necessary to keep the bar at equilibrium.

    *** On edit ***
    Are we to assume that gravity acts on this bar?
    Last edited: Sep 14, 2011
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook