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Homework Help: Vector Problem-Direction and Magnitude

  1. Sep 9, 2007 #1
    1. The problem statement, all variables and given/known data
    Determine the magnitude of the resultant force Fr=F1+F2 and its direction measured from the positive u axis.

    2. Relevant equations
    Law of Sines?

    3. The attempt at a solution
    I drew parallel lines and attempted to use the sine law, but I got two different answers.
    Here's the equations I used:
    Fr/sin100 = 200/sin50
    Fr/sin100 = 300/sin30


    Using these equations, I got two different answers for Fr, and didn't get any direction.

    Other than what I tried, I don't know what to do. We weren't taught how to find the magnitude from components or taught how to find direction.

    Attached Files:

    Last edited: Sep 9, 2007
  2. jcsd
  3. Sep 9, 2007 #2
    can't see your images, can you link it instead?
  4. Sep 9, 2007 #3
    Yes, sir.
  5. Sep 10, 2007 #4


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    Homework Helper

    The problem is that you're assuming F1 + F2 ends up along the u axis... it doesn't.
  6. Sep 10, 2007 #5
    I have to use the angles to figure out which direction the resultant force is pointing after [tex]F_1[/tex] and [tex]F_2[/tex] are added, but I don't know how.
  7. Sep 10, 2007 #6


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    Homework Helper

    The things you know for sure are the 200, 300 sides... and the 100 degrees angle. You can use those to get the magnitude of F1+F2, and the angles....

    Draw a triangle separately from the axes... when you get the angles... then you can draw F1+F2 in correctly...
  8. Sep 18, 2007 #7
    Ok, thank you sir.
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