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Homework Help: What am I doing wrong on this Statics Problem?

  1. Jan 26, 2015 #1
    1. The problem statement, all variables and given/known data
    I signed up for Mechanics of Materials, but it turns out my statics is very rusty. Here is the problem, we are to compute the six component forces about the joints:


    2. Relevant equations
    Force and moment equations are the name of the game.

    3. The attempt at a solution

    My problem arises thusly:

    I sum the moment about A. I place: C_x(.6)+(B_y).8=0. We know from the diagram that b_yu = 30. Simply solve this equation, and the result is C_x = 40. This is correct, according to the book.

    Now, I go to sum the moments about B, C_x(.6)+A_y(.8)=0. This yeilds A_y =30. According to the book A_u=0. What is invalid about my approach?

    Thanks a ton.
  2. jcsd
  3. Jan 26, 2015 #2
    Your equation assumes C_y is zero.

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