Question

A man swims with a speed of $4km/h$ in still water. The speed of the river is $3km/h$. He starts swimming in the river perpendicular to the direction of the flow of the current of the river. The river is $2km$ wide. What is the horizontal shift of the man?

• A. $0.75km$
• B. $1.5km$
• C. $2km$
• D. $1km$

Answer 1

The correct option is B $1.5km$

Speed of man, $v_m=4km/h$
Speed of river, $=v_r=3km/h$
Width of river, $s=2km$
The time taken by the man to cross the river $=\frac{s}{v_m}=\frac{1}{2}hr$
In this same time the man has also travelled a horizontal distance due to the velocity of the river.
Distance travelled due to the velocity of the river $=v_r\times t=1.5km$
Hence the correct option is (b).