Question

HEY FOLKS

A river is flowing from west to east at speed of v= 5 m/s a man on the south bank of the river capable of swimming at 10 m/m in still water ; wants to swim across the river in shortest time . he should swim in a direction

[a ] due north [b] 30° east of north [c] 30°north of east [d] 60 °east of north

Answer 1

Person should across the direction of flow of river
Answer=due north

Answer 2

Answer _ a. due north

Because
Velocity of man in River
= Velocity of man + Velocity of River

if man starts to swim in the river at an angle b from the river bank ,
Resultant velocity
= Vm sin (b) i +( VM cos(b) + V river )j
i- velocity towards north
j - velocity towards east

for Shortest time we need to increase the velocity towards north

Therefore , Vm sin b should be of max value
sin b should be of max value
b = 90 degrees
which is north