Question

A man can row a boat at $4km/h$ in still water. What is the minimum possible time in which he can cross the river if the speed of the current is $4km/h$ and the width of the river is $8km$?

• A. $1h$
• B. $2h$
• C. $\sqrt{3}h$
• D. $\sqrt{2}h$

Answer 1

The correct option is B $2h$

For minimum time man must row the boat perpendicular to the river flow.

From the figure,
time $=\frac{d}{v_{mr}}$
$⟹\frac{8}{4}=2h$