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Question:

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?

150o

90o

60o

120o

Solution:

Correct option is D. 120o
For swimmer to cross the river straight ⇒ 4sin θ = 2 ⇒ sin θ = 1/2 ⇒ θ = 30o
So angle with direction of river flow = 90o + θ = 120o