# Problem regarding sounds and waves

## Homework Statement

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?

## 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.

## Answers and Replies

Doc Al
Mentor
Well I know that, d=vt
That's really all you need.

I can't even understand why I'll hear two sounds at other end for the first case
Because sound travels both in the iron of the pipe and in the water filling the pipe.

Thanks for the reply Doc Al. Well that solves the first question but you didn't say anything about the second one or maybe you did and I'm not getting it. Please reply, I'm not that bright.

Doc Al
Mentor
What do you think? Compare the second with the first. Any fundamental difference?

Oh I'm really really sorry. I left out an important part of the question. In the second question, it should've been 'If the pipe is 400 meters long and 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?'