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Homework Help: Displacement vectors

  1. Feb 13, 2008 #1
    1. The problem statement, all variables and given/known data
    Vector A is 3 m and vector b is 3m. The angle formed by the positive x axis is 30°. Find A +B

    2. Relevant equations

    3. The attempt at a solution

    Does this look correct?


    Vector A+B=(3cos30 +3cos30)+(3sin30+3sin30)

    magnitude=square root((3cos30 +3cos30)^2+(3sin30+3sin30)^2)
    =square root(27+9)=6


    and if it were vector A-B, the only difference would be that you would take (3cos30+3cos30)+(-3sin30-3sin30) and the magnitude would be square root of (3cos30+3cos30^2)+(-3sin30-3sin30)^2 right?

    Thank you very much
    Last edited: Feb 13, 2008
  2. jcsd
  3. Feb 13, 2008 #2
    I have no Idea what you mean by this.
  4. Feb 13, 2008 #3
    Sorry.The angle formed by the two vectors on the positive x axis is 30°. Can you tell me if I did this correctly? Would the magnitude of vector A+B be the square root of (3cos30+3cos30)^2+(3sin30+3sin30)^2

    Would the magnitude of A-B be:
    square root of (3cos30+3cos30)^2+(3sin30+3sin30)=


    But they shouldn't be the same, right? Do you see where I went wrong?

    Thank you
    Last edited: Feb 13, 2008
  5. Feb 14, 2008 #4
    That still doesn't tell me where A and B point.
    The magnitude of A+B can only be 6 if A and B point in the same direction however, and then of course A+B would have the same direction as A And B and then A-B would be the 0 vector, so your answer can't be right.
    The easiest way to do this is to compute the components of A and B in the X and Y directions, then add them, and then convert back to a magnitude and direction.
  6. Feb 14, 2008 #5
    Thank you very much

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