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Homework Help: Bending Moment in two directions

  1. Sep 14, 2011 #1
    Not Really a homework question but it will help with how i go about the homework.

    So i have a beam coming out of the wall and it has force acting on it like this:
    Woops, that 20 on the side view should be a 10 :P
    What i want to find is the total moment at the mid point. I know how to find the moment in each direction but im not sure if im aloud to add them together or use pythag??
    heres my solution for each direction:
    Can i just go sqrt(10^2+10^2) to give me 10?
  2. jcsd
  3. Sep 14, 2011 #2


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    Hi Shaun, welcome to PF!
    Moments are vectors and as such, have both magnitude and direction. So aside from the fact that sqrt(10^2+10^2) = 10(sq root 2) :wink:, its magnitude, there is a direction associated with the moment also (what is it?). Sometimes it is best to leave the moment in its component form....M = Mx + My.
  4. Sep 14, 2011 #3
    thanks heaps mate, probably shouldnt be doing engineering if i cant use pythag properly :tongue:
    really appreciate ur help
  5. Sep 14, 2011 #4
    In your M diagrams, the horizontal one shows an assumed hinge at the wall, whereas the vertical one assumes moment-fixity. This may not affect your answer to the moment at midpoint of the beam.
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