(1) From the topic, it can be known that the time when particle D first arrives at the trough is 0.05s earlier than that when particle E first arrives at the trough, indicating that the velocity direction of point D is downward at this time. Then, according to the wave translation method, the wave propagates in the positive direction of the X axis, with the wave period of t = T=4×0.05s=0.2s, the wavelength λ=4m and the wave velocity of v = λ t = 20m/s in the figure.

(2) When the particle is transmitted to the particle B at the time x=- 1m, the particle B moves downwards through the equilibrium position, and the distance from x=- 1m to x= 1.5m is x=2.5m, so the shortest time for the particle B to move downwards through the equilibrium position is t = XV = 2.520s.

The equilibrium position of particle b is x = l.5m, and according to mathematical knowledge, the ordinate y of particle b is -522cm. .

Since t=0. 125s=58T, we can know from the wave translation method that the shortest time for particle b to reach the equilibrium position is 18T, and the distance traveled by particle b in this time is S = | y |+2a = (10+522) cm.

Answer: ① The propagation direction of this series of waves propagates along the positive direction of the X axis, with a wave speed of 20? Postgraduate students.

② After at least 0. 125 s, particle 6 moves downward through the equilibrium position, and the distance traveled by particle B during this time is (10+522)? centimetre