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River Boat Question That's Throwing Me Off

  1. Feb 10, 2015 #1
    1. The problem statement, all variables and given/known data
    A river flows due north with a speed of 2.90 m/s. A man rows a boat and reaches the opposite shore right across its initial position; his velocity relative to the water is 5.50m/s. His landing point is due east relative to its initial location. The river is 1000 m wide.
    a). What is his speed relative to the earth?
    b.) At what angle does he travel relative to the eastern direction?
    c.) At what angle does he aim the boat relative to the eastern direction?
    d.) How much time is required to cross the river?
    e.) How far north of his starting point will he reach the opposite bank?


    2. Relevant equations
    Vbg2=Vbr2+Vrg2

    t=ΔX/Vbr

    Distance=Speedavg x t


    3. The attempt at a solution I had a similar problem before this one but this specifies that he reached the opposite shore right across from his initial position which is throwing me off.
    a.) 5.52+2.92=√38.66 -> 6.22 m/s
    b.) Wasn't sure how to even do this for this question
    c.) ^ ditto
    d.) t=1000/5.5= 181.82 s
    e.) Distance= 2.9 x 181.52 s = 527.28 m

    Unfortunately those were all wrong :(
     
  2. jcsd
  3. Feb 10, 2015 #2

    Nathanael

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    Homework Helper

    Using pythagorean's theorem to add vectors only works if they are perpendicular. So if the man pointed his boat directly east (which is perpendicular to north) then your answer for the speed would be correct.
    However the man does not point his boat directly east.
    The man points his boat in such a way that "his landing point is due east relative to his initial position."
    So what does this mean about part (e)? And what about part (b)? (Do those two parts first, they require no calculations.)
    Then do part (c) then do part (a) then do part (d).
     
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