^Crossing a river
Suppose a person start rowing his boat from point O with velocity vbr (w.r.t. river i.e. without considering the effect of water) towards point S in order to cross a river of width ‘w’ flowing at a speed ‘vr’ towards x axis. Let under the effect of river current boat has net velocity the boat vb (w.r.t. ground i.e. resultant vbr & vr) & he reaches point R, then the distance SR covered downstream (i.e. distance along the stream) is called drift.