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3D Statics Help

  1. Aug 26, 2014 #1
    1. The problem statement, all variables and given/known data
    If the coordinate direction angles for F3 = 650lb are α = 110∘, β = 25∘ and γ = 76∘, determine the magnitude of the resultant force acting on the eyebolt.

    FIGURE: p80.jpg


    2. Relevant equations
    ????


    3. The attempt at a solution
    ????

    New semester, and so happy to start with a statics instructor I can't understand or follow . . . I seriously don't even know where to begin and neither does anyone else (we've tried lots, multiple times). I know there's some formulas like cos^2α + cos^2β + cos^2γ = 1 or something, but I don't even know where I would start.
     
  2. jcsd
  3. Aug 26, 2014 #2

    Zondrina

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    The direction angles are related to the resultant force and axial components by the relationships:

    ##cos(\alpha) = \frac{F_{3_x}}{F_3}##
    ##cos(\beta) = \frac{F_{3_y}}{F_3}##
    ##cos(\gamma) = \frac{F_{3_z}}{F_3}##
     
  4. Aug 26, 2014 #3
    Ah, learning more here than so far in class. Love it. Using those relationships, I got the vector components of F3, and using trig, got the vector components of F1 and F2, added the components together, and took the magnitude. Done √.

    And the rest of the problem is just asking for alpha, beta, and gamma, which I now know! Thanks! I'll probably be back with a new thread in a bit unless the next problem uses the same relationships . . .
     
  5. Aug 30, 2015 #4
    How did you get the vector components of F1?
     
  6. Aug 30, 2015 #5
    To find F1
    700cos(30)= 606 i
    700sin(30)= 350 j
    700cos(90)= 0 k
     
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