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Homework Help: Average velocity problem

  1. Sep 16, 2010 #1
    1. The problem statement, all variables and given/known data

    A car travels east at 95 km/h for 1.5 hours. It then travels 30.0° east of north at 111 km/h for 1.8 hours.

    What is the average velocity for the trip? (Magnitude and degrees)


    2. Relevant equations

    law of cosines/resultant

    3. The attempt at a solution

    I have tried doing this:
    d=952 + 1112 - 2(85*111)cos60 = 110km
    v=110km / 3.3 hr = 33.1 m/s

    for the angle...
    tanx = Bsinx/ a + bcosx = 111sin60/95+111cos60 = 0.638
    x = 32.5 north of east

    Both of these were wrong...any help please??
     
    Last edited: Sep 16, 2010
  2. jcsd
  3. Sep 16, 2010 #2

    diazona

    User Avatar
    Homework Helper

    You have basically the right idea to use the law of cosines, but this step is wrong. If you include the units in the calculation, you will see why.
     
  4. Sep 16, 2010 #3
    Nvm, I see now.
     
    Last edited: Sep 16, 2010
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