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: Need help clarifying statics problem.

  1. Jul 30, 2012 #1


    1. The problem statement, all variables and given/known data
    What is the magnitude of the internal force in member BC?

    2. Relevant equations
    So I figured out the reaction force at A and D by taking the moments about point A to find the vertical force at D and then summing the x and y components to find the forces at A.

    3. The attempt at a solution

    So I solved for the reaction forces for A, and D already. Why can't I split the truss into three members? Why can't I take member AD and have a free body diagram for that member and solve for the Fx and Fy for Bx and By by summing the forces? Do I absolutely have to take the moment? Can I not do


    To find the components of B? This method doesnt seem to work.
    Why do I have to take the moment?
  2. jcsd
  3. Jul 30, 2012 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    This is not a pure truss since the horizontal and vertical members are subject to bending. When taking a FBD of AD, you must include the horizontal component of force at D, found by first taking a FBD of the vertical member.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook