The siren on an ambulance is emitting a sound whose frequency is 2250 Hz. The sp

Question

The siren on an ambulance is emitting a sound whose frequency is 2250 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 26.5 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 26.5 m/s and you are moving toward it at a speed of 13.0 m/s, find the wavelength and frequency of the sound you hear.

Explanation / Answer

By doppler effect,

f' = fo(v + vL) / (v - vS)

and

wavelength' = v / f'

Thus:

A. vL = vS = 0, hence,

f' = 2350 Hz   [ANSWER]
wavelength' = 0.146 m [ANSWER]

************

B.

f' = 2547 Hz   [ANSWER]
wavelength' = 0.1347 m   [ANSWER]

********************

c.

f' = 2651 Hz
wavelength' = 0.1294 m   [ANSWER]

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