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Homework Help: Help! river crossing confusion =(

  1. Feb 7, 2005 #1
    Woo. Nevermind the rest of this message. I figured it out =))))



    Hello all :)

    Am having brain fart, I need help (obiviously) from the experts! All the tutorials and examples about the classic boat crossing a river aren't helping me with this problem.

    "A woman can row a boat at 6.3 km/h in still water. (Assume i points to the far side of the river, perpendicular to the current, and j points in the direction of the current.)"

    At this point, I drew a diagram. As for vectors, i is 105 m/min [answers require meters/minutes] perpendicular to shore, I assumed current to be heading east (downriver in my drawing).
    ___________________________________
    ......^.........105 m/min i.......................|
    ......| ............................................5500m
    ......|................................................|
    .....--------> 0 m/min j....................|

    This makes sense, b/c it would take roughly 52 mins to cross to a point directly across. Then comes the confusing bits.....

    (a) If she is crossing a river where the current is 3.2 km/h, in what direction must her boat be headed if she wants to reach a point directly opposite her starting point? (in degrees)

    (b) How long will it take her to cross the river? (in minutes)


    Based on the above, i is still 105 m/min and j is now ~53.3 m/min, so the resultant would be 117.5 m/min.... I think.
    From there, I'm lost. Please help!

    -Jen
     
    Last edited: Feb 7, 2005
  2. jcsd
  3. Feb 7, 2005 #2
    90 degrees- tan-1(6.3/3.2)

    is the angle
     
  4. Feb 7, 2005 #3
    what your email and ill send you a good diagram
     
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