question_answer

The stream of a river is flowing with a speed of 2km/h. A swimmer can swim at a speed of 4km/h. What should be the direction of the swimmer with respect to the flow of the river to cross the river straight? [JEE Main 9-4-2019 Morning]

A) \[60{}^\circ \]                       

B) \[150{}^\circ \]

C) \[90{}^\circ \]                       

D) \[120{}^\circ \]

Correct Answer: D

Solution :

For swimmer to cross the river straight \[\Rightarrow 4\sin \theta =2\]\[\Rightarrow \sin \theta =\frac{1}{2}\Rightarrow \theta ={{30}^{o}}\] So, angle with direction of river flow \[=90{}^\circ +\theta =120{}^\circ \] Option [d]