will add more points if answers are correct, promise. A person standing a certai
ID: 2243245 • Letter: W
Question
will add more points if answers are correct, promise.
A person standing a certain distance from an airplane with four equally noisy jet engines is feeling a sound level intensity bordering on pain. 127 dB. What sound level intensity would this person experience if the captain shut down all but one engine? If one sound is 24 dB greater than another sound, what is the ratio of their intensities (greater/smaller)? Tsunamis are fast-moving waves generated by underwater earthquakes. In the deep ocean their amplitude is barely noticeable, but upon reaching shore, they can rise up to the astonishing height of a six-story building. One tsunami, generated off the Aleutian islands in Alaska, had a wavelength of 850 km and traveled a distance of 3700 km in 5.5 h. Find the wave's frequency. Sound propagating through air at 32 degree C passes through a vertical cold front into air that is 3.7 degree C. If the sound has a frequency of 2100 Hz. by what percentage docs its wavelength change in crossing the boundary? 10. What would be the intensity level of a 49-decibel sound after being amplified a million times?Explanation / Answer
6.You need to divide the power level by 4, however you must use the logrithm rules as well as the fact that dB = 10*log base 10 (power) so
10 log( power / 4) = 10 log(power) - 10 log(4)
we already have 10 log(power) = 127 so we figure out that 10 log(4) = 6.02 So the dB power of 1 engine would be
127 - 6 = 121 dB
7.)greater!
db = 10 log I / Io = 24
I / Io = 10^(24/10) =10^(2.4)
8.)speed = 3700*1000 / (5.5*3600)
speed = 3700000 / 19800
speed = 198 m/s to two significant figures.
f = c / ?
f = 198 / 850000
f = 2.32 * 10^-4 Hz to two significant figures.
9.)Since the frequency of the sound will not change, the wavelength change will depend only on the change in the speed of sound.
The speed of sound is given by:
c = sqrt(gamma*k*T/m)
(where gamma is the adiabatic gas constant, k isboltzmann constant T is absolute temperature (Kelvin), m = average molecular mass). For our atmosphere, this can be approximated as:
331.3 + (0.606)*T-c (see reference)
- So at 32 degrees C it will be: 350.692 m/s
- And at 3.7 degrees C it will be: 333.5422 m/s
Therefore, the percentage change in the wavelength is the percentage change in the speed of sound, which is:
100* [333.5422 - 350.692) / (350.692)]
= -4.89 %
10)1 million = 10^6, so the answer is 49 + 60 = 109dB
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