Question
A boat which has a speed of $$5\,km/hr$$ in still water crosses a river of width $$1\,km$$ along the shortest possible path in 15 minutes. The velocity of the river water in $$km/hr$$ is
A.
$$3$$
B.
$$4$$
C.
$$\sqrt {21} $$
D.
$$1$$
Answer :
$$3$$
Solution :
Speed along the shortest path $$ = \frac{1}{{\frac{{15}}{{60}}}} = 4\,km/hr$$
Speed of water $$v = \sqrt {{5^2} - {4^2}} = 3\,km/hr$$
Speed along the shortest path $$ = \frac{1}{{\frac{{15}}{{60}}}} = 4\,km/hr$$
Speed of water $$v = \sqrt {{5^2} - {4^2}} = 3\,km/hr$$
