A swimmer can swim at 5 m/s relative to water. A river flows at 3 m/s and is 80 m wide. The swimmer chooses his direction so that he reaches the point directly opposite. The crossing time is:
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A swimmer can swim at 5 m/s relative to water. A river flows at 3 m/s and is 80 m wide. The swimmer chooses his direction so that he reaches the point directly opposite. The crossing time is:

G1 Physics · Accepted Answer

For zero drift, the upstream component is 3 m/s. Therefore the cross-river component is √(5² - 3²) = 4 m/s. Thus t = 80/4 = 20 s.