Q. A river is flowing from $W$ to $E$ with a speed of $\ 5\ m/min$. A man can swim in still water with a velocity $10\ m/min$. In which direction should the man swim so as to take the shortest possible path to go to the south
A) $30{^\circ}$ with downstream
B) $60{^\circ}$ with downstream
C) $120{^\circ}$ with downstream
D) South
Explanation
(c) For shortest possible path man should swim with an angle $(90 + \theta)$ with downstream
From the fig,
$\sin\theta = \frac{v_{r}}{v_{m}} = \frac{5}{10} = \frac{1}{2}$
$\Rightarrow \ \therefore\ \theta = 30{^\circ}$
So angle with downstream $= 90{^\circ} + 30{^\circ} = 120{^\circ}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.