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Homework Help: This is an engineering statics question, I need help on trig

  1. Sep 11, 2011 #1
    1. If cylinder E weighs 30lb and theta = 15 degrees, determine the weight of cylinder F

    2. Sigma F = 0 (Statics question)

    3. I have gotten my separate components but I don't know how to solve the equations this sounds really stupid since I'm in calc III and physics II but my brain is just crapping out on me.

    I have attached a sketch of the problem
    The only thing(s) that are given are the three angles, and one weight.

    I am having a hard time figuring out how to solve these equations.

    So far I have
    Sum(x) = 0 = -Fab cos30 + Fbc cos15
    Sum(y) = 0 = Fbc sin30 - 30 - Fab sin15

    I even have the solutions on hibbeler however I want to learn how to solve these equations, its definitely a basic concept that I should know how to do, that is solving trig problems.

    Attached Files:

  2. jcsd
  3. Sep 11, 2011 #2
    Can you solve the first equation for [itex]F_{ab}[/itex] in terms of [itex]F_{bc}[/itex]? Once you do that, you should be able to plug that into the second equation and solve for [itex]F_{bc}[/itex].
  4. Sep 12, 2011 #3
    Even with opposite signs /components?
    I will try
    Thank you

    For the FBD on knot B
    Can I not use the properties of angles that are symmetrical about a line segment to assume that Fcb cos 15 = 30cos15?

    Actually in the physical sense that's not correct seeing as there is another tension force on the other side of knot b.

    Attached Files:

    Last edited: Sep 12, 2011
  5. Sep 12, 2011 #4
    I think I've got it, I just hit a dumb wall of "I can't do trig even though I'm in calc III"
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