Question

The stream of a river is flowing with a speed of $2 \, km \, h^{- 1}$ . A swimmer can swim at a speed of $4 \, km \, h^{- 1}$ . The direction of the swimmer with respect to the flow of the river, to cross the river straight, is

• A. $150^\circ $
• B. $90^\circ $
• C. $120^\circ $
• D. $60^\circ $

Answer 1

Answer: (C)

To reach the point directly opposite to the starting point, the resultant velocity of swimmer should be as shown in figure.

From figure
$sin \theta =\frac{2}{4}=\frac{1}{2}$
$\theta =30^\circ $
Angle with flow $=90^\circ +30^\circ =120^\circ $