Need some Physics help

[mrSHEiK124]

A semi-detailed solution would be appreciated 🙂

It has been suggested that US military tests of a powerful form of sonar (SURTASS-LFA) was responsible for the deaths of quite a few whales some years ago. This device produces under water sound waves with a logarithmic intensity of ~235 dB as measured at 1 m from the source. What is the amplitude of the pressure wave at 500 m from the source?

I was trying to use an impulse formula with the speed of sound in water (1.4 * 10E5 m/s) but I got lost.

 

[Brutus04]

If I told ya I'd have ta kill ya. Very large though...and very low freq.

 

[theflyingpig]

I got lost too. Sorry.

 

[Greenman]

Proly be better off asking the whales.

 

[jagec]

Originally posted by: Greenman
Proly be better off asking the whales.

"Sir, could you give me an estimate of the diameter of the bullet that hit you?"

 

[Rubycon]

Text

 

[Born2bwire]

Usually it would depend upon the frequency I would think.

Edit: Hmmm.. nevermind, I don't think water would be lossy enough to make the frequency matter too much. The main mechanism of loss is going to be the spatial loss, the 1/r^2 law.

 

[mrSHEiK124]

Originally posted by: Rubycon
Text

Thanks! 235 dB at 1 m is 181 dB at 500 m, according to the calculator. But, we're doing this in water, won't the difference in the speed of sound affect it?

 

[mrSHEiK124]

last bump

 

[Rubycon]

Hopefully this can help.

 

[mrSHEiK124]

Got a 100 on the exam 😀

Converting to W/cm2 means I can cross multiply distances/intensities to find the intensity at whatever distance I want. Then I can use sqrt(2 * density of medium * speed of sound in medium * intensity) to get the pressure/amplitude in some weird unit, and divide by 10 to get Pa 🙂