Question

The stream of a river is flowing with a speed of $2\text{km/h}$. A swimmer can swim at a speed of $4\text{km/h}$. What should be the direction of the swimmer with respect to the flow of the river to cross the river straight ?

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

Answer 1

The correct option is B ${120}^{\circ }$


To cross the river straight
$V_s\sin \theta =V_r$
$\therefore \sin \theta =\frac{V_r}{V_s}=\frac{2}{4}=\frac{1}{2}$
$\therefore \theta ={30}^{\circ }$
Direction of swimmer with respect to flow
$={90}^{\circ }+{30}^{\circ }={120}^{\circ }$
Hence option $\left(C\right)$ is correct.