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Unit Vector Help

  1. Oct 12, 2009 #1
    1. The problem statement, all variables and given/known data
    Find the magnitude and direction of A + B for the following vectors.

    A = -4 i - 1 j, B = 8 i -2 j

    How do I find the magnitude of A+B, and also the degree clockwise from the +x direction?
     
  2. jcsd
  3. Oct 12, 2009 #2

    berkeman

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    Staff: Mentor

    You add the components to get the resultant, which is also in rectangular coordinates. Do you know how to convert the resultant vector from rectangular coordinates to polar coordinates (so you can get the resultant magnitude and direction)?
     
  4. Oct 12, 2009 #3
    So would it be 4i - 3j? On my webassign homework, it has to be a single numerical value.
     
  5. Oct 12, 2009 #4

    berkeman

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    Staff: Mentor

    That's the correct answer in rectangular coordinates. If they are asking for a single number for an answer, did you say they want the angle that the vector forms with some axis? A vector is always made up of 2 numbers (in 2 dimensions). In rectangular coordinates, it's the i and j components. In polar coordinates, it's the magnitude and direction (usually the direction is the angle swinging up from the x axis to the vector).

    Do you know how to convert the vector from rectangular to polar coordinates? That should be in your book.
     
  6. Oct 12, 2009 #5
    Got it. Thanks man!
     
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