1, "crossing the river along the shortest path" refers to the river bank perpendicular to the speed direction, so it is required that there is no speed in the current direction, that is to say, the ship speed is decomposed into a speed along the current direction to offset the current speed, and the bow should be inclined upstream. According to the decomposition and synthesis of motion, let the included angle between the bow and the current direction be a, 0.5*cosa=0.3, then A is 37, that is, the bow and the current form an angle of 37. At this time, the speed used to cross the river is the fractional speed of the ship perpendicular to the river bank, that is, 0.5 * sin37 = 0.4m/s. Since the fractional motion and the combined motion are isochronous, the time t= 120/0.4=300s.

2. The shortest crossing time is to use all the speed of the ship to cross the river. At this time, the bow should be perpendicular to the river bank. At this time, because the ship participates in two movements, one is downstream and the other is perpendicular to the river bank, and these two movements are independent and do not interfere with each other, so the shortest time is t= 120/0.5=240s.