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Homework Help: Relative velocity boat crossing a river

  1. Mar 16, 2013 #1
    1. The problem statement, all variables and given/known data
    A boat crosses river, 240 m wide,which flows parallel to the straight banks with velocity
    v1 = 12i, while the velocity of the boat relative to the river is v2 = 5j where v1 and v2 are measure in m/s

    (i) find the magnitude of the actual velocity of the boat.

    (ii) find how long it takes the boat to cross the river and the distance it has travelled downstream in doing so

    2. Relevant equations

    3. The attempt at a solution
    (i)(12^2 + 5^2)^(1/2) = 13 m/s

    (ii) relative distance/relative speed = 240/5 =48 s

    48(12) =576 m

    can somebody tell if part (ii) is right the back of my book seems to use 12 as the relative speed since it says it takes 20 seconds.
    Any help would be appreciated.
  2. jcsd
  3. Mar 16, 2013 #2


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    Homework Helper

    Your solution is correct.

  4. Mar 16, 2013 #3


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    Science Advisor
    Homework Helper

    yes, it looks as if the book has got the 12 and the 5 the wrong way round :redface:
  5. Mar 16, 2013 #4
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