Question

A 30 meter wide canal is flowing at the rate of 20 m/min. A boy can swim at the rate of 25 m/min in still water. The time taken by him to cross the canal perpendicular to
the flow is

Answer 1

To have a velocity directly across relative to land, the boy must aim upstream relative to the water.

25 m/min is the vector sum of 20 m/min along the river flow and 15 m/min straight across, because
25^2 = 15^2 + 20^2

The time required to swim 30 m across is
t = 30/ 15 = 2 minutes.

Answer 2

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