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Question involving velocities and distance

  • #1

Homework Statement


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?


Homework Equations


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


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!
 

Answers and Replies

  • #2
tiny-tim
Science Advisor
Homework Helper
25,832
250
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:
 
  • #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?
 
  • #4
tiny-tim
Science Advisor
Homework Helper
25,832
250
(just got up :zzz: …)
I tried doing vector addition and ended up with a relative velocity of 8.17 m/s …
ahh … for relative velocities, try vector subtraction! :wink:
 

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