Question

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

Answer 1

Correct Answer - b
`t=d/(sqrt(v^(2)-u^(2)))`

`implies 15/60=1/(sqrt(5^(2)-u^(2))) implies u=3km//h`