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Homework Help: I'm having trouble trying to solve this particular problem.

  1. Jan 28, 2010 #1
    1. The problem statement, all variables and given/known data

    A car makes a trip due north for three-fourths of the time and due south one-fourth of the time. The average northward velocity has a magnitude of 13 m/s, and the average southward velocity has a magnitude of 11 m/s. What is the average velocity (magnitude and direction) for the entire trip?

    2. Relevant equations
    not sure

    3. The attempt at a solution

  2. jcsd
  3. Jan 28, 2010 #2
    If I walk forward 2 miles in half an hour, and then walk backwards 1 mile in half an hour, how far have I walked forward and how long did it take me?
  4. Jan 28, 2010 #3
    1 mile and 1 hour
  5. Jan 28, 2010 #4
    1 mile and 1 hour
  6. Jan 28, 2010 #5
    So your average velocity is one miler per hour in the forward direction, right? Use that same logic for your problem. Your average speed is close to 12 m/s (actually 12.5, since you were going 13 m/s for a longer time than you were going 11 m/s), but your average velocity has a direction associated with it. You were going 12.5 m/s on average, but you weren't going that fast north.
  7. Jan 28, 2010 #6
    okay I understand its northward, but the part I don't get is what formula to use?
  8. Jan 28, 2010 #7
    You basically just need to do the same simple algebra we did in my example. The only difference is that I gave you distances and time instead of velocity. It's a lot easier than you think. Try a few samples using different values of time and see what you get.
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