Question

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° with downstream
• B. 60° with downstream
• C. 120° with downstream
• D. South

Answer 1

Answer: (C)

120° with downstream

Answer 2

For shortest possible path man should swim with an angle (90+θ) with downstream.

From the fig, $\sin\theta = \frac{v_{r}}{v_{m}} = \frac{5}{10} = \frac{1}{2}$ ⇒ $\therefore$ θ = 30°

So angle with downstream = $90{^\circ} + 30{^\circ} = 120{^\circ}$