# Finding the Depth of Water

1. Feb 13, 2008

### zachcumer

[SOLVED] Finding the Depth of Water...

Hello, Can you guys help me? I have to answer this question for Physics Class: "An oceanic depth-sounding vessel surveys the ocean bottom with ultrasonic sound that travels 1530 m/s in seawater. How deep is the water if the time delay of the echo from the ocean floor is 6 s?"

Last edited: Feb 13, 2008
2. Feb 13, 2008

### Hootenanny

Staff Emeritus
Yes we can help you, but you need to show us what you know first.

P.S. Please don't use large fonts, it's unnecessary and won't get your question answered any faster.

3. Feb 13, 2008

### zachcumer

Well, what I tried was thinking that it takes three seconds to get to the floor of the ocean and then three seconds to get back. Six seconds total. So I tried 1530 times 6...thats wrong...

4. Feb 13, 2008

### zachcumer

also I know that speed of sound travels 345 meters per second...but don't think that applies here..

5. Feb 13, 2008

### Hootenanny

Staff Emeritus
How far has the sound waves traveled in six seconds? Is is the depth of the ocean or ...?
Indeed you are correct, that is the speed of sound in air, but we're in water here.

6. Feb 13, 2008

### zachcumer

345 times 6 is 2040...

7. Feb 13, 2008

### Hootenanny

Staff Emeritus
I refer you to my previous post, you do not want to use 345 m/s, that is the speed of sound in air, not water. I repeat by previous question from the pulse leaving the boat, hitting the ocean floor and then returning to the boat, how far has it traveled?

8. Feb 13, 2008

### zachcumer

so 12 seconds...what?

9. Feb 13, 2008

### Hootenanny

Staff Emeritus
1. The sound wave is emitted from the boat
2. The sound wave travels through the water to the ocean floor
3. The sound wave is then reflected off the ocean floor
4. The sound wave travels from the ocean floor to the boat
5. The time taken for this entire journey is 6 seconds.
You want to know that distance between the boat and the ocean floor.

10. Feb 13, 2008

### zachcumer

yes. right. thats where I get stuck.

11. Feb 13, 2008

### zachcumer

wait...1530 times 6 seconds equals 9180...hmmm

12. Feb 13, 2008

### Hootenanny

Staff Emeritus
So if the whole journey takes six seconds, how long does the journey from the boat to the ocean floor take?

13. Feb 13, 2008

### zachcumer

9180 meters

14. Feb 13, 2008

### Hootenanny

Staff Emeritus
????

15. Feb 13, 2008

### zachcumer

So if the whole journey takes 6 secs. 1530 meters per second. 1530 times 6? no?

16. Feb 13, 2008

### Hootenanny

Staff Emeritus
If the whole journey takes six seconds, how long does it take for the sound to travel from the boat to the ocean floor only, i.e. half the journey.

17. Feb 13, 2008

### zachcumer

3 seconds.

18. Feb 13, 2008

### Hootenanny

Staff Emeritus
Correct , so the distance from the boat to the ocean floor is...

19. Feb 13, 2008

### zachcumer

4590 meters!

20. Feb 13, 2008

### Hootenanny

Staff Emeritus
Correct ! The key point to note here is that the time delay measured is the time taken for the sound waves to travel twice the depth of the ocean (down and then back up).