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Homework Help: Why did we assume it to be 45 degrees?

  1. Mar 9, 2012 #1
    1. The problem statement, all variables and given/known data
    a motorist drives south at 20 m/s for 3 min, then turns west and travels west at 25m/s for 2 min, and finally travels n/w at 30 m/s for 1 min. for this 6 minute trip, find the net vector displacement

    2. Relevant equations

    3. The attempt at a solution

    distance 1: 20m/s * 3min * 60s/min = 3600m south
    distance 2: 25m/s * 2.6min * 60s/min = 3900m west
    distance 3: 30m/s * 1min * 60s/min * cos45 = 1273m west
    ................ 30m/s * 1min * 60s/min * sin45 = 1273m north

    My real problem is why we assumed the angle is 45 degrees? Why did we dissect the 90 degree angle in half for the north west if it doesnt tell us in the problem?
  2. jcsd
  3. Mar 9, 2012 #2

    Doc Al

    User Avatar

    Staff: Mentor

    It says that it travels n/w = northwest, which means half-way between North and West. That's where the 45 degrees comes in.
  4. Mar 9, 2012 #3
    thank you!
  5. Mar 9, 2012 #4
    In the problem statement it says "travels west at 25m/s for 2 min" yet in your attempt at a solution you change it to 2.6 min. Why?
  6. Mar 9, 2012 #5
    just a silly typo sorry
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