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The width of a river is 100 m. The speed of the ship in still water is 5 m / s. The speed of the current is 3 M / s 1. How to cross the river in the shortest time 2. How to cross the river with the shortest displacement Is it perpendicular to the river bank?
The shortest time should be that the ship's speed is perpendicular to the river bank, and the time is 100 / 5 = 20s
The shortest displacement should make the combined speed of ship speed and water speed perpendicular to the river bank. When the combined speed is 5 and water speed is 4, it just forms a right triangle. Therefore, the combined speed is 4, the shortest displacement is 100m, and the time is 100 / 4 = 25s
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