1) A jet engine emits sound uniformly in all directions, radiating an acoustic p

Question

1) A jet engine emits sound uniformly in all directions, radiating an acoustic power of 3.79 × 105 W. Find the intensity of the sound at a distance of 42.5 m from the engine and calculate the corresponding sound intensity level. A) Find intensity __________ W/m^2 B) Find intensity level __________ dB

2) You are walking along a small country road one foggy morning and come to an intersection. While you are crossing, you hear an ambulance siren. As a paramedic, you know that the siren sounds at a frequency of 7.47 kHz. But, as an amateur musician with perfect pitch, you can tell that the frequency you are hearing is actually 7.93 kHz. Is the ambulance moving toward or away from you? At what speed is the ambulance traveling? _______ mph

Explanation / Answer

1)

intensity = power/area
A)

I = P/(4pir^2) = (3.79*10^5)/(4*pi*42.5^2) = 16.7 W/m^2

B)

threshold intensity = 10^-12

intenswity level = 10*log(I/Io) = 10*log(16.7/10^-12) = 132.22 dB

+++++++

2)

as the heard frequency is greater than actual , the ambulance is moving towards

f' = f*v/(v-vs)

7930 = (7470*343)/(343-vs)

vs = 19.9 m/s

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