If you stand in front of a corrugated pipe culvert at position A
(see the figure at right) and clap your hands, creating a sharp
pulse of sound, the reflections off the corrugations
(spaced 10 cm apart) will return to you at different
times, creating a distinctive sound.
Taking into account the lateral dimensions of the culvert,
sketch the resultant wave amplitude s(t)
detected at position A as a function of time t
and calculate the dominant frequency of the reflected sound
just before it becomes inaudible.