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Homework Help: Parallelogram Law of Vector Addition

  1. May 1, 2008 #1
    1. The problem statement, all variables and given/known data

    I'm having trouble with a word problem involving the parallelogram law of vector addition. The problem reads as follows:

    Two forces with magnitudes 8N and 11N act on a large object. The angle between the forces is 30 degrees.

    a) Draw a diagram to represent the combined effort of the forces.b) Calculate the magnitude of the resultant force.

    2. Relevant equations

    Not sure.

    3. The attempt at a solution

    a) I drew the 8N vector horizontal and the 11N 30 degrees from the horizontal. Both vectors are tail-to-tail.

    b) I know that I'm supposed to use the parallelogram law of vector addition, complete the parallelogram and the resultant vector will share the same tail with my original two vectors and the head of the resultant vector will be at the opposite vertex of the parallelogram.

    I just don't know how to do the actual calculation, which is where I need the help.
  2. jcsd
  3. May 1, 2008 #2


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    Homework Helper

    if I call the horizontal the "x-axis" then the x-component of the 8N force is 8N and the y-component of the 8N force is zero.

    what are the x and y components of the 11N force? you will need to use trig.
  4. May 1, 2008 #3


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    P.S. this should probably be posted in the introductory physics forum not the "calculus and beyond" forum... but whatever.
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