A boat which has a speed of `5 km` per hour in still water crosses a river of width 1 km along the shortest possible path in fifteen minutes. The velocity of the river water in km per hour is :-

Options

A. 1
B. 3
C. 4
D. `sqrt((41))`

Answer

2

Explanation

`t=(d)/(sqrt(v^(2)-u^(2)))`
`(15)/(60)=(1)/(sqrt(5^(2)-4^(2)))`
`v_(r)=sqrt(5^(2)-4^(2))=3km//h`