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Homework Help: Vector Direction on XY Plane

  1. Sep 29, 2015 #1
    1. The problem statement, all variables and given/known data
    The drawing shows two cars traveling in different directions with different speeds. Their velocities are:
    vAG = velocity of car A relative to the Ground = 27.0 m/s, due east
    vBG = velocity of car B relative to the Ground = 21.0 m/s, due north
    The driver of car B looks out the window and sees car A. The velocity of car A relative to car B is vAB. The angle that the velocity vAB makes with respect to due east is?

    2. Relevant equations

    3. The attempt at a solution
    I got the correct angle which is 37.9 degrees, however the answer says 37.9 degrees south of east. HOW IS IT SOUTH OF EAST?? I'm so confused, why is it not north of east? The angle is made by going 37.9 degrees NORTH of the horizontal east axis so why in the world is the answer south of east, I just do not understand.

    Attached Files:

  2. jcsd
  3. Sep 29, 2015 #2


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    If you were in car B, is car A receding from you? If it is receding and you're traveling north, what direction of travel would you see for car A?
  4. Sep 29, 2015 #3
    So since car B is traveling north, it's perspective of car A is technically south?
  5. Sep 29, 2015 #4


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    Yes, think about it. If your frame of reference is car B, car A appears to be traveling south east as it's both receding from your frame, and traveling eastward.
  6. Sep 29, 2015 #5
    Okay that makes more sense. Thank you!
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