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Homework Help: Quick 2d motion question

  1. Sep 22, 2008 #1
    1. The problem statement, all variables and given/known data

    A hunter wishes to cross a river that is 1.5 km wide and flows with a speed of 5.0km/h parallel to its banks. the hunter uses a small powerboat that moves at a maximum speed of 12 km/h with respect to the water. What is the minimum time necessary for crossing?

    3. The attempt at a solution

    5km/h^2 + 12Km/h^2=sq rt 169km/h^2 = 13 km/h

    The hunter moves really moves at 13 km/h to the right because of the water moving upstream. 13 is the vector resultant of 5 north and 12 east.

    So, T=D/V

    T=width of stream/velocity of hunter
    T=1.5km/12km/h = 0.125 h
  2. jcsd
  3. Sep 22, 2008 #2


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    You calculate the correct velocity of the hunter (V = 13 km/h), but when you calculated his time of crossing you used V = 12 km/h.
  4. Sep 22, 2008 #3
    If I used 13km/h instead of 12km/h, would the answer be right?
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