Question

A man can swim at a speed 2 m/s in still water. He starts swimming in a river at an angle 150 to the direction of water flow and reaches the directly the directly opposite point on the opposite bank.
(a) Find the speed of flowing water.
(b) If width od river is 1 km then calculate the time taken to cross the river.

Answer 1

Here $V_R=$ velocity of river

$V_M=$ velocity of man in still water = 2m/s (given)

from figure it is clear that

$\sin \theta =\frac{V_R}{V_M},$ where $\theta =60$ degree

$⟹V_R=\sqrt{3}m/s$

from figure it is evident that

$V_M\cos \theta \times t=1000m$

$⟹t=1000$ s