Question

A river is flowing from west to east at a speed of 5 metres per minute. A man on the south bank of the river, capable of swimming at 10 metres per minute in still water, wants to swim across the river in the shortest time. He should swim in a direction.
(a) due north
(b) 30° east of north
(c) 30° north of west
(d) 60° east of north.

Answer 1

Answer:

he should swim towards east

Answer 2

A river is flowing from west to east at a speed of 5 metres per minute. A man on the south bank of the river, capable of swimming at 10 metres per minute in still water, wants to swim across the river in the shortest time. He should swim in a direction (a) due north

Explanation:

• If a man moves in a corner from east to north, although his relative speed is increasing, he has to travel a greater distance. It will take more time.

• When a man swims in a corner from west to north, his relative speed decreases. It will take more time.

Time taken to reach the opposite bank = $\frac{d}{10 sin\theta}$

where d = width of river

Therefore the correct answer is Option (a) due north