Width L = 300m, river velocity V1 = 3m / s, ship velocity V2 = 5m / s in still water, find: (1) what is the shortest time for the boat to cross the river? What is the course of the boat? (2) what is the shortest displacement for the boat to cross the river? What is the time for the boat to cross the river?

Width L = 300m, river velocity V1 = 3m / s, ship velocity V2 = 5m / s in still water, find: (1) what is the shortest time for the boat to cross the river? What is the course of the boat? (2) what is the shortest displacement for the boat to cross the river? What is the time for the boat to cross the river?

This topic is a bit deep, not as simple as it seems
(1) In fact, the condition of water velocity is ignored when crossing the river, and the shortest time is L / V2 = 60s;
The course of the boat is 53 ° to the shore (according to Pythagorean theorem)
(2) If the shortest displacement is needed, then the direction of the boat is perpendicular to the direction of the water flow. Let this velocity be v3,
Then (V3) &# 178; = (V2) &# 178; - (V1) &# 178;, we get V3 = 4m / s
So the shortest displacement of crossing the river is 300m, and the time is 300 / 4 = 75s
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