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Homework Help: Addition of a System of Coplanar Forces

  1. Sep 15, 2010 #1
    1. If the problem statement, all variables and given/known data

    The resultant force acting is directed along the positive x-axis, determine the magnitudes of F2 and the resultant force

    And that F3x=4 and that F3y=3 (its a right angle 3-4-5 triangle)

    2. Relevant equations
    F1=F1x +F1Y
    F2=F2x +F2Y
    F3=F3x +F3Y

    3. The attempt at a solution
    F1y= 4cos(30) = 3.464

    And since the resultant force is along the x-axis, the resultant y force (Fry) would therefore have to equal 0.

    But when you run the numbers:

    Fry=(+3.464)N + (-3)N + F2y
    F2y= -0.464

    But that is impossible because F2 is above the x-axis and therefore couldn't have a negative y value.

    This is where I am currently stuck, if it would work out i could figure out the resultant of F2y and F2x which would be F2, and the find out the resultant of all three from there on.

    Thank you in advance,
  2. jcsd
  3. Sep 15, 2010 #2


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    Staff Emeritus
    Science Advisor
    Gold Member

    Welcome to PF,

    How do you know that F3 is 30 degrees from the x-axis? Your diagram doesn't indicate such.
  4. Sep 16, 2010 #3
    I don't, I just know that it is a 3-4-5 triangle.

    I know that F2 is 30 degrees away from the x-axis though
  5. Sep 16, 2010 #4
    Well, this is embarrassing.
    My friend who I was working on it with and I both failed to see the direction of the arrow F1...
    As it is pointing downwards, not upwards, this question makes a lot more sense now...

    Sorry for your time!

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