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Homework Help: Mechanics of Materials - Internal Moment

  1. May 18, 2009 #1
    1. The problem statement, all variables and given/known data

    Hi everyone. I am attempting to calculate the internal moment at point B about the y-axis. I have correctly found everything else.


    My calculations:
    Weight of 500mm section of pipe = 58.9N
    Weight of 400mm section of pipe = 47.1N
    Vertical reaction at A = 58.9 + 47.1 = 106N

    2. Relevant equations

    Moment = Force x Distance

    3. The attempt at a solution


    I'm not really sure I can do that with the two 60N forces, but I also can't see why not.
    The correct answer is 6.23Nm according to the solutions provided.

    Any help would be greatly appreciated!
  2. jcsd
  3. May 18, 2009 #2
    For the portion of the tube along the X axis due to the tube weight

    Moment at B = (1/2)*g*12*(0.2)^2 = 2.35 Nm

    For the downward 60N force

    Moment at B = 0.05*60 = 3.0 Nm

    For the rod portion along the Y axis

    Moment at B = 0.2*0.4*g*12 = 9.41 Nm

    For the upward 60N force

    Moment at B = -0.35*60 = -21 Nm

    Total moment at B = 2.35+3.0+9.41-21 = -6.24 Nm, where -ve sign CCW direction
  4. May 18, 2009 #3
    Overt - Thankyou very much for the reply, I'll go and work through your solution now. It seemed like a pretty straight forward problem so it's been annoying me all day!

    Much appreciated,
  5. May 18, 2009 #4


    User Avatar
    Science Advisor
    Homework Helper

    What does "-ve" in post 2 mean? Where is its definition? Could not find it in an on-line dictionary. Could you point me to an on-line source that defines it?
  6. May 18, 2009 #5


    User Avatar
    Gold Member

    -'ve = negative, + 'ive = positive , its shorthand notation
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