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Finding magnitude of two forces with given degrees ?

  1. Nov 29, 2009 #1
    1. The problem statement, all variables and given/known data

    Two forces F1 and F2 are applied, F1 makes a 45 degree angle and F2 makes a 30 degree angle. The resultant R has a magnitude of 500 lbf and acts along the positive x-axis. Determine the magnitudes of F1 and F2.

    2. Relevant equations
    Pythagorean theorem?

    3. The attempt at a solution
    I thought using the pythagorean theorem would be used for this problem.
    c^2=a^2 + b^2 - 2ab cos C

    somebody pleaseeee help me :S
    Last edited: Nov 29, 2009
  2. jcsd
  3. Nov 29, 2009 #2


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    Homework Helper

    Welcome to PF, Kari.
    Yes, not all that clear, is it? I think it means F1 is angled 45 degrees up from the x-axis and F2 is 30 degrees below the x-axis.
    Sketch that! Let us label the magnitude of F1 as "a" and the magnitude of F2 as "b".

    Two other facts are given.
    1. the sum of the vectors is along the x-axis, so the sum of the y components is zero.
    2. the sum of the x-components is 500.

    Write an equation for each of those facts, based on your diagram, and you will be able to solve them as a system of 2 equations to find the magnitudes a and b.
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