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A person aiming to reach exactly the opposite point on the bank of a stream is swimming with a speed of 0.5 m/s at an angle of 120° with the direction of flow of water. The speed of water in the stream is

Asked in NEET 1999 · River and boat problems

Answer: (1) 0.25 m/s

Step-by-step solution

Given: swimmer at 0.5 m/s, heading 120° from the downstream direction, and reaching the point directly opposite.

Idea: landing directly opposite means the net velocity is straight across, so the swimmer's upstream component must exactly cancel the stream.

The component of his velocity along the flow is 0.5 cos 120°=-0.25 m/s, that is 0.25 m/s upstream.

For the net drift to vanish, the stream must supply 0.25 m/s downstream.

v_water=0.25 m/s.

Why the other options are wrong

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