The speed of a swimmer is 4 km h−1 in still water. If the swimmer makes his strokes normal to the flow of river of width 1 km, he reaches a point 750 m down the stream on the opposite bank.
The speed of the river water is _____ km h−1.
Answer: 3
Solution
Pointing his strokes straight across, the swimmer crosses the 1 km width at his own speed of 4 km h−1, taking t=41 h. In that same time the current carries him 750 m =0.75 km downstream, and this drift is produced entirely by the river's flow, so vr=tdrift=1/40.75=3 km h−1.
JEE Main · 2023 · 31 Jan 2023 · Shift 1 · Integer answer