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Vectors: Given displacement and direction. Erroneously obtaining opposite values.

  1. Sep 1, 2012 #1
    1. The problem statement, all variables and given/known data

    A person walks 25 degree north of east for 3.10 km. How far would another person have to walk due north and due east to arrive at the same location?

    2. Relevant equations
    sin = opp/hyp
    cos = adj/hyp


    3. The attempt at a solution
    I drew a line representing north of east 3.10 km at 25 degrees.
    ....
    ../.
    ./..
    /...

    I then drew the lines for north and east

    /\--->
    |.../
    |../
    |./

    I used sin 25 = opp/3.10
    and cos 25 = adj/3.10

    and I came up with the values 1.31 for east and 2.81 for north.

    However, the correct answer is 1.31 north and 2.81 east, my values were mixed up.
    Can someone explain to me where I went wrong and why this is the right answer? I assumed the bottom most point on my sketch as where the 25 degrees NE, because it seemed to be going in that direction at that point.
     
  2. jcsd
  3. Sep 1, 2012 #2
    You drew east of north instead of north of east.

    "25 degress north of east" = start at east and turn 25 degrees towards north
     
  4. Sep 1, 2012 #3
    You drew east of north instead of north of east.

    "25 degress north of east" = start at east and turn 25 degrees towards north
     
  5. Sep 2, 2012 #4
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