The siren on an ambulance is emitting a sound whose frequency is 2150 Hz. The sp

Question

The siren on an ambulance is emitting a sound whose frequency is 2150 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 26.3 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 26.3 m/s and you are moving toward it at a speed of 12.0 m/s, find the wavelength and frequency of the sound you hear.

Explanation / Answer

n = 2150 Hz
c = n = 343 m/s

a )
= 343/ 2150 = 0.16 m .
n = 2150 Hz

b)
Source is moving and observer is at rest.
n’ = c n /(c-Vs) = 343 * 2150/ ( 343 – 26.3) = 2328.5 Hz
= 343/ 2328.5 = 0.147m

c)
Source and observer are moving toward each other
n’ = ( c + Vo) n /(c-Vs) = ( 343 + 12)* 2150 / ( 343 – 26.3)
n’ = 2410 Hz
= 343/ 2410 = 0.142 m

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