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Question
A swimmer wishes to cross a 500 m wide river flowing at 5 km/h. His speed with respect to water is 3 km/h. Find the shortest possible time to cross the river.
Solution
Shortest possible time to cover the river:
Take θ = 90∘
\[\text{ Time } = \frac{0 . 5}{3\sin\theta} h = \frac{500 \times 6}{5\sin\theta} = \frac{600}{\sin90^\circ} s = 600 s\]
Hence, the required time is 10 minutes.
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