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^@` west of north
D. `60^@` east of north.

Answer 1

Correct Answer - A
a. Time taken to cross the river ` t= d/(v_scostheta)`
For time to be minimum, `cos theta = max rArr theta = 0^@`

Hence, the swimmer should swim due north.