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Homework Help: Question involving velocities and distance

  1. Mar 28, 2010 #1
    1. The problem statement, all variables and given/known data
    Two soccer players, Mary and Jane, begin running from nearly the same point. Mary runs in an easterly direction at 4 m/s, while Jane takes off in a direction 60 degrees north of east at 5.4 m/s. (a) How long before they are 25 m apart? (b) What is the velocity of Jane relative to Mary? (c) How far apart are they after 4 s?


    2. Relevant equations
    D=v/t
    Yf=Yi+(Vy)iT+1/2at^2
    Xf=Xi+(Vx)iT


    3. The attempt at a solution
    T must be the same value in both equations, but I do not know how to convert velocity vectors with a 60 degree separation into distance to solve the problem. I have a test tomorrow and your input would be much appreciated!
     
  2. jcsd
  3. Mar 28, 2010 #2

    tiny-tim

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    Welcome to PF!

    Hi drummerdimitr! Welcome to PF! :smile:

    (try using the X2 tag just above the Reply box :wink:)

    Hint: If you can answer (b) first, then (a) should be easy. :wink:
     
  4. Mar 28, 2010 #3
    Thanks for the quick reply, I found the answer to part c by multiplying the velocities by 4 and finding the length of the third side. I tried doing vector addition and ended up with a relative velocity of 8.17 m/s at 34.9 degrees north degrees, but unfortunately, it is not the right answer. What am i doing wrong here?
     
  5. Mar 29, 2010 #4

    tiny-tim

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    (just got up :zzz: …)
    ahh … for relative velocities, try vector subtraction! :wink:
     
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