Question

A swimmer can swim in still water with a speed of .$\sqrt{5}$ m/s. While crossing a river his average speed is 3 m/s. If he cross the river in the shortest possible time, what is the speed of flow of water?

• A. 2 m/s
• B. 4 m/s
• C. 6 m/s
• D. 8 m/s

Answer 1

Answer: (A)

2 m/s

Given : $V_{SR}=\sqrt{5}$ m/s $V_S=3$ m/s

Let the speed of flow of water be $V_R$

$\therefore$ $V_S^2=V_{SR}^2+V_R^2$

OR $3^2=(\sqrt{5}{)}^2+V_R^2$

$\therefore$ $V_R^2=4$ $⟹V_R=2m/s$