An ambulance has a siren with frequency 2600 Hz. If you are stationary and the a

Question

An ambulance has a siren with frequency 2600 Hz. If you are stationary and the ambulance is heading away from you at 45 m/s, what frequency do you hear? The speed of sound in the air is 338 m/s. 2,946 Hz 2,999 Hz 2,600 Hz 2,254 Hz 2,295 Hz A person sits 90 m away from an exploding firecracker and measures the sound level to be 70 dB. What is the total power of the sound emitted by the firecracker? Assume that the sound radiates equally in all directions from the firecracker. 23.61 W 0.339 W 1.018 W 3.054 W 20.56 W

Explanation / Answer

28) E)2295 Hz

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

= 2600*338/(338 + 45)

= 2295 hz

29) C) 1.018 W

Let I is the intensity of sound at person location.

apply

beta = 10*log(I/Io)

70 = 10*log(I/10^-12)

7 = log(I/10^-12)

10^7 = I/10^-12

==> I = 10^(7 - 12)

I = 10^-5 W/m^2

Apply, I = power/Area

I = P/(4*pi*d^2)

==> P = I*4*pi*d^2

= 10^-5*4*pi*90^2

= 1.018 Watts

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