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. 2
C. 3
D. `sqrt(41)`

Answer

C

Explanation

`s=ut`
`1=v_(BR) cos theta t`
`1=5 cos theta 1/4`
`cos theta=4/5 rArr theta=37^(@)`
`v_(R)=v_(BR) sin 37^(@)=5xx3/5=3 km//hr`