Question #aea85

1 Answer
P dilip_k
Oct 26, 2016

Since the boat crosses the river of width 1km along the shotest possible path in 15min or 0.25hr, its resultant velocity of crossing the river will be #V_"cross"=1/0.25=4" km/hr"#.This velocity will be perpendicular to the direction of the velocity of river #V_"river"#. Given the velocity of boat in still water #V_"boat"=5" km/hr"#

Obviously

#V_"boat"^2=V_"river"^2+V_"cross"^2#

#=>5^2=V_"river"^2+4^2#

#V_"river"=sqrt(5^2-4^2)=3" km/hr"#

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