1. The problem statement, all variables and given/known data An iron pipe is 1200 meters long and is filled with water. If a sound is made at one end of the pipe, two sounds/noises are heard at the other end. If the speed of sound in water is 1450 m/s and the speed of sound in iron is 5220 m/s then Q(1) : How long is it gonna take to hear the second sound at the other end after the first one? Q(2) : If the pipe is filled with air in which the speed of sound is 340 m/s, will making a sound at one end produce two sounds at the other end? 2. Relevant equations 3. The attempt at a solution Well I know that, d=vt and in the case of echo it's 2d=vt but in this case, it's no echo and there are two mediums here which is confusing me and I can't even understand why I'll hear two sounds at other end for the first case.