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Vector direction help

  1. Sep 17, 2007 #1
    ive been trying to do this problem but i dont know where to start....any help?


    let v be a vector of length 9 in the direction 65degrees south of west.

    if u has the same direction as v, and if 3|u| = 2|v|, then which of the following can be used to describe u?


    u = 5.705i + 12.235j
    u = -2.536i - 5.438j
    u = 2.536i + 5.438j
    u = -5.705i - 12.235j
    none of these
     
  2. jcsd
  3. Sep 17, 2007 #2

    radou

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    Are you sure about that?
     
  4. Sep 17, 2007 #3
    no im not sure....cause im not even sure how to get started on this question...
     
  5. Sep 17, 2007 #4

    radou

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    Draw your vector v down, first. Do you know anything about projections on the x and y axis?
     
  6. Sep 17, 2007 #5
    yeah
    i think i have to find the components of u but using the magnitude of v..is that right?
     
  7. Sep 17, 2007 #6

    radou

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    First of all, you have to write down v in the form v = ___ i + ___ j. Then, you know that 3|u| = 2|v|, eg |u| = 2/3|v|.
     
  8. Sep 17, 2007 #7
    okay thanks i think i got it now : )
     
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