物理(波動)(10分)

(a) Time needed = distance/speed = 5/2 s = 2.5 s
(b) Yes. Because there would be a phase change of 180 degrees on reflection at the tree. The pulse thus travels backward on the right side along the spring. Time needed = (2.5 + 1/2) s = 3 s

(c) A longitudinal wave (縱波) is produced. The pulse will clear with the signboard.