# Finding the Depth of Water

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?"

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

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

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...

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

Staff Emeritus
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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...
How far has the sound waves traveled in six seconds? Is is the depth of the ocean or ...?
also I know that speed of sound travels 345 meters per second...but don't think that applies here..
Indeed you are correct, that is the speed of sound in air, but we're in water here.

zachcumer
345 times 6 is 2040...

Staff Emeritus
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345 times 6 is 2040...
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?

zachcumer
so 12 seconds...what?

Staff Emeritus
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so 12 seconds...what?
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.

zachcumer
yes. right. that's where I get stuck.

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

Staff Emeritus
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yes. right. that's where I get stuck.
So if the whole journey takes six seconds, how long does the journey from the boat to the ocean floor take?

zachcumer
9180 meters

Staff Emeritus
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9180 meters

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

?

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

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

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

zachcumer
3 seconds.

Staff Emeritus