The siren on an ambulance is emitting a sound whose frequency is 2750 Hz. The sp

Question

The siren on an ambulance is emitting a sound whose frequency is 2750 Hz. The speed of sound is 343 m/s. (a) If the ambulance is stationary and you (the "observer") are sitting in a parked car, what are the wavelength and the frequency of the sound you hear? (b) Suppose that the ambulance is moving toward you at a speed of 26.8 m/s. Determine the wavelength and the frequency of the sound you hear. (c) If the ambulance is moving toward you at a speed of 26.8 m/sand you are moving toward it at a speed of 12.0 m/s, find the wavelength and frequency of the sound you hear.

I just cannot get the answer to part C

Explanation / Answer

Here ,

a) when both the person and ambulance are at rest

frequency , f = f0

f = 2750 Hz

the frequency of the sound is 2750 Hz

-------------

as frequency * wavelength = speed

2750 * wavelength = 343

wavelength = 0.125 m

the wavelength is 0.125 m

b)

for the ambulance , vs = 26.8 m/s

v = 343 m/s

f = f0 * (v + vs)/v

f = 2750 * (343 + 26.8)/343

f = 2964.9 Hz

the frequency of the wave is 2964.9 Hz

wavelength will be constant ,

wavelength = 0.125 m

the wavelength is 0.125 m

c)

for the moving frequency

for the ambulance , vs = 26.8 m/s

v = 343 m/s

f = f0 * (v + vs)/(v - 12)

f = 2750 * (343 + 26.8)/(343 - 12)

f = 3072 Hz

the frequency of the wave is 2964.9 Hz

wavelength will be constant ,

wavelength = 0.125 m

the wavelength is 0.125 m

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