A Swimmer Can Swim In Still Water With A Speed Of 5 Ms–1. While Crossing A River His Average Speed Is 3 Ms–1. If He Crosses The River In The Shortest Possible Time, What Is The Speed Of Flow Of Water?

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Question

A swimmer can swim in still water with a speed of 5 ms^–1. While crossing a river his average speed is 3 ms^–1. If he crosses the river in the shortest possible time, what is the speed of flow of water?

easy

Solution

Correct option is

4 ms^–1

In order to cross the river in the shortest time, the resultant velocity v of the swimmer must be perpendicular to the velocity v_w of water. It follows from the figure that

= 25 – 9

= 16