What am I doing wrong on this Statics Problem?

  • Thread starter k_squared
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Homework Statement


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:

twY08aU.png


Homework Equations


Force and moment equations are the name of the game.

The Attempt at a Solution


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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.
 

Answers and Replies

  • #2
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4,605
Your equation assumes C_y is zero.

Chet
 

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