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It is known that the width of the river is 300 m, the flow velocity is 1 m / s, and the velocity of the ship in still water is 3 M / s (1) Crossing the river in the shortest time; (2) crossing the river with the least displacement; (3) Reach 100m downstream of the opposite bank; (4) reach 100m upstream of the opposite bank These four conditions are used to calculate: the degree of the angle between the ship's course and the upstream opposite bank? The time to cross the river? Let v 1 be the velocity passing through the flow direction, V 2 be the velocity perpendicular to the flow direction, and t be the time to cross the river V1²+V2²=3² （V1+1)*t=100 t=300/V2. The same as (3): V1 & sup2; + V2 & sup2; = 3 & sup2; (v1-1) * t = 100, t = 300 / V2, t =? α =? Can you explain in detail, especially the three energies 3 & sup2; in V1 & sup2; + V2 & sup2; = 3 & sup2? Thank you very much for your answer, sincerely ask!
(1) The angle is 0 ° t = 300 / 3 = 100s (2) the minimum displacement is 300m, which is the width of both sides of the river. Therefore, the speed of the ship sailing against the water in the direction opposite to the flow direction should be equal to the flow speed. If the angle is 1m / s, cos α = 1 / 3
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