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Calculating vector components (displacement, oooh)

  1. Feb 5, 2014 #1
    1. The problem statement, all variables and given/known data

    Sophie walks 800 M [N], then 500 M [W] and finally 400 M [SE] in 25 minutes. What is her displacement and average velocity? (Using scale diagram)

    2. Relevant equations

    a2 + b2 = c2

    3. The attempt at a solution

    I tried calculating by creating separate triangles, but was not certain what to do with the 400 M [SE] as I was not given an angle.

    This was my attempt, assuming that both south and east are 400 M

    Y = 800 north - 400 south = 400 M north
    X= -500 or 500 west + 400 east = -100 or 100 west

    Using Pythagorean theorem, I calculated for size Z and got 412.3 M
    Then moving forward from that to calculate the direction, I said tan-1 (100/400) equals 14 degrees.

    My final answer was 412.3 M [W 14 degrees N]

    Now I also do not have an answer key and this is an assignment that I can't figure out. Any help would be appreciated, thank you!
  2. jcsd
  3. Feb 5, 2014 #2
    You do have the angle for 400 m [SE]. They mean she was traveling EXACTLY south east. That direction is 45 degrees from south and 45 degrees from east.

    You made another mistake. 400 m south east is not the same as 400 m south then 400 meters east. You need to use the pythagorean to break 400 m [SE] into south and east components.
  4. Feb 5, 2014 #3

    I just tried it and it makes much more sense now! Thanks again!
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