A fire truck has a 1200 Hz siren. The speed of sound in air is 343 m/s. If the fire truck is traveling at 35 m/s away from a stationary observer, what frequency of sound will the observer hear? How does this relate to the doppler effect?
Please show process, more interested in knowing how it is done. Will be quick to award BA, thanks in advance for any help.
Please show process, more interested in knowing how it is done. Will be quick to award BA, thanks in advance for any help.
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this is a problem involving the doppler effect
if the vehicle is receding, the wavelength will become longer and the frequency smaller; we can calculate this from the doppler effect equation
f(observed) = c/(c+V) x f(source)
where f(observed) is the frequency measured by the observer, c is the speed of sound, V is the speed of the vehicle, and f(source) is the frequency in the reference frame of the siren
note the plus sign in the denominator, that is the form for the source receding; if the person were moving toward the source, there would be a negative in the denominator
we have then
f(observed) = 343m/s / (343m/s + 35m/s) x 1200Hz
f(obs) = 1089Hz
if the vehicle is receding, the wavelength will become longer and the frequency smaller; we can calculate this from the doppler effect equation
f(observed) = c/(c+V) x f(source)
where f(observed) is the frequency measured by the observer, c is the speed of sound, V is the speed of the vehicle, and f(source) is the frequency in the reference frame of the siren
note the plus sign in the denominator, that is the form for the source receding; if the person were moving toward the source, there would be a negative in the denominator
we have then
f(observed) = 343m/s / (343m/s + 35m/s) x 1200Hz
f(obs) = 1089Hz