The width of the river is 200m, the static water speed of the ship is 5m / s, the water speed is 3m / s, the shortest time to cross the river? The shortest time for the ship to cross the river? The moving distance along the downstream when it is perpendicular to the opposite bank Seeking solution urgently

The width of the river is 200m, the static water speed of the ship is 5m / s, the water speed is 3m / s, the shortest time to cross the river? The shortest time for the ship to cross the river? The moving distance along the downstream when it is perpendicular to the opposite bank Seeking solution urgently

The shortest time should be that the relative speed is perpendicular to the bank, i.e. the bow is perpendicular to the bank,
So t = 200 / 5 = 40s
The shortest distance should be that the absolute velocity is perpendicular to the river bank, and the angle between the bow and the river bank is less than 90 degrees. At this time, the absolute velocity is v ^ 2 = 5 ^ 2-3 ^ 2, v = 4m / s
Therefore, t = 200 / 4 = 50s
When perpendicular to the opposite bank (i.e. the first case), the moving distance along the downstream is s = 40s * 3m / S = 120m
This is the problem of relative motion in physics