The width of the river is 300 m, the flow velocity is 3 M / s, and the velocity of the boat in still water is 5 m / s, Q: (1) what is the shortest time to cross the river? Where can I get to the other bank? (2) Where should the bow of a boat cross the river on the shortest voyage? What is the crossing time?

The width of the river is 300 m, the flow velocity is 3 M / s, and the velocity of the boat in still water is 5 m / s, Q: (1) what is the shortest time to cross the river? Where can I get to the other bank? (2) Where should the bow of a boat cross the river on the shortest voyage? What is the crossing time?

(1) In the shortest time, the ship speed is used for crossing. 300 △ 5 = 60s, which is washed down 60 × 3 = 180m in the 60s. At 180m downstream of the opposite bank of the river (2), the shortest distance is perpendicular to the river bank. Part of the ship speed is used to offset the water speed, and the other part is used to draw a vector parallelogram, which is a right angle with 3 right sides and 5 oblique sides