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Homework Help: Vectors-magnitude problem

  1. Sep 15, 2013 #1
    A man in search of his dog drives first 12.7 mi northeast, then 17.7 mi straight south, and finally 7.97 mi in a direction 30.3° north of west.

    a) What is the magnitude of his resultant displacement?

    okay so i wont explain everything i did but im pretty sure i got the right numbers.
    for my resultant vector i get (2.09899, -4.63). the magnitude should be 5.08357. but its somehow not the right answer and im not sure what i did wrong.

    whats weird is that i needed to find the position of this vector which would be arctan(2.09899/-4.63) + 360. which would be 294.07136 degrees. THIS IS THE CORRECT ANGLE!! so then wouldn't that mean that (2.09899, -4.63) are the right x and y values?!?!?

    what am i doing wrong?

    thanks for any help!!
  2. jcsd
  3. Sep 15, 2013 #2


    Staff: Mentor

    I'd start by drawing a picture and solving it graphically and then see if your numbers agree.

    Don't forget you need to follow the PF homework template and show some intermediate work before we can help.
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