The first question: from A to B, downstream, the actual speed of the ship in the water is V static +V water; From b to a, countercurrent, the actual speed of the ship in the water.

The degree is V static -V water. The same is the distance between terminals a and b.

According to S=Vt, 2 (static+water) = 2.5 (static-water), water = 3 km/h.

∴V Static = 27km/h

The second question: For the first time, the distance between Party A and Party B is 36km, and they each drive for 2 hours, but they haven't met yet; The second time, the distance between Party A and Party B is 36 kilometers, which is their own.

After driving for 4 hours, they were 36 kilometers apart after meeting. During the whole process, the distance between a and b remains the same.

∴ Let the distance between A and B be S, then

2(V A +V B) +36=S

4(V A +V B) -36=S

∴: The answer is S =108km.

Question 3: If the length of the train is L and the speed is V, then the distance it travels completely through the tunnel must be the length of the tunnel+the length of the train, that is,

(L+300)m, and the distance traveled by the lamp irradiation is the train length l,

∴20V=300+L

10V=L

∴ It is concluded that the train speed V=30m/s and the train length L=300m.