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How To Find Depth Given TIME ONLY

1. Homework Statement
The time it takes a high frequency sound to travel from the surface of the lake to the bottom of the lake and back to the surface is 0.1seconds. What is the depth of the lake?


2. Homework Equations
Speed of sound in water= 1500m/s
Time=0.1s
Depth=?


3. The Attempt at a Solution
Depth= Speed of sound * time elapsed/2= 1500*0.1/2
= 75m
IS THIS CORRECT? PLEASE HELP?
 

phyzguy

Science Advisor
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Looks good to me!
 
Really? I assumed that 1500 m/s was the speed of sound in water. Didn't know if it was correct since it wasn't given to me in the question... Can u help me with another question please?
 
Really? I assumed that 1500 m/s was the speed of sound in water. Didn't know if it was correct since it wasn't given to me in the question... Can u help me with another question please?
 

phyzguy

Science Advisor
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Oh, I assumed you were given the speed of sound in water at 1500 m/s, but it still looks good, since Wikipedia says the speed of sound in water is 1484 m/s (http://en.wikipedia.org/wiki/Speed_of_sound). What is your other question?
 
Oh, I assumed you were given the speed of sound in water at 1500 m/s, but it still looks good, since Wikipedia says the speed of sound in water is 1484 m/s (http://en.wikipedia.org/wiki/Speed_of_sound). What is your other question?
Thanks.
The other question is:
A ship is 220metres from a large cliff when it sounds its foghorn. If the echo time is 0.5s, how far is the ship from the cliff?

I don't understand what to do.
 

phyzguy

Science Advisor
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It's conceptually the same as the first one. Treat it the same way. What is an echo?
 
It's conceptually the same as the first one. Treat it the same way. What is an echo?
An echo is a repeated sound caused by the reflection of sound waves from a surface. I still don't get what to do :(

Should I multiply 220 by the 0.5? :/
 
Last edited:

phyzguy

Science Advisor
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An echo means the sound went from the ship to the cliff, was reflected from the cliff and traveled back to the ship, where it was heard. Does this help?
 
An echo means the sound went from the ship to the cliff, was reflected from the cliff and traveled back to the ship, where it was heard. Does this help?
I understand that but I just don't know how to work it out.. would the distance be the same?
 

phyzguy

Science Advisor
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How far does the sound have to go to go from the ship to the cliff and back?
 

phyzguy

Science Advisor
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If the ship is 220 meters from the cliff, how far does the sound have to go to go from the ship to the cliff and back?
 
440 metres?
 

phyzguy

Science Advisor
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OK, good. Now how fast is the sound traveling (remember it is in air)? And given this, how long will it take?
 

DaveC426913

Gold Member
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1] this was posted elsewhere and,
2] taken as-is, it's a trick question. The answer is provided in the question.
 

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