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

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A

$60^\circ$

27%

B

$150^\circ$

8%

C

$90^\circ$

13%

D

$120^\circ$

53%

Solution:

For swimmer to cross the river straight
$\Rightarrow \, \, 4 sin \theta = 2$
$\Rightarrow \, \, sin \theta = \cfra{1}{2} \Rightarrow \, = $ 30°
So, angle with direction of river flow = 90° + $\theta$ =
120°
Option (4)

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