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Homework Help: Statics problem

  1. Apr 19, 2006 #1
    hey all. I'm having problems with what should be a simple statics problem.

    "The Magnitude of force F is 80.0 N. What are the madnitude of its components a) F\ab and b) F\ac that are paralell to the bars AB and AC respectively."

    The picture: Force F pointing straight down. bar AB pointing 30 left of straight up (NW), and and bar AC pointing 70 degrees left of straight up (NW also).

    I know i need to use the dot product somehwhere, but I can't determine what i need to do it with respect to. But I did rotate the problem 90 degrees CCW, and had the resulting equation:

    |80*F\ac|cos110 + |80*F\ab|cos150=0

    additional question: will F\ab + F\ac = 80. When adding up all those forces this problem doesn't seem to be in static equallibrium....

  2. jcsd
  3. Apr 19, 2006 #2
    No, adding the force onto each bar will not equal the original force.

    Each component part of your equation is right, but I do not understand why you are trying to add the components. When you see a force written as F=#i+#j, the 'i' and 'j' are 90 degrees apart.
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