Drift is distance along a river a boat covers in crossing the river. If the boat reaches point C, distance BC is called downstream drift and if the boat reaches point D, distance BD is called upstream drift. To cross a river without drift, what should be relation between `v_(br)` and `v_(r)` and `v_(r)`. If a boat crosses a river without drift, in which direction must it be steered.

Answer

`v_(br) gt v_(r), theta=sin^(-1) (v_(r)/v_(br))` upstream of line AB