A boat which has a speed of `5 km// hr ` in steel 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

Options

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

Answer

B

Explanation

`v_(B//W)sintheta=V_(W)`
`(1)/(4)=(1)/(V_(B//W)costheta)`
`V_(B//W)costheta=4`
`costheta=(4)/(5)`
`theta=37^(@)`
`5 sin37^(@)=V_(W)`
`V_(W)=3km//hr`