The siren on an ambulance is emitting a sound whose frequency is 2650 Hz. The sp

Question

The siren on an ambulance is emitting a sound whose frequency is 2650 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 26.1 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 26.1 m/s and you are moving toward it at a speed of 11.0 m/s, find the wavelength and frequency of the sound you hear.

Explanation / Answer

n = 2650 Hz

c = n = 343 m/s

a )

= 343/ 2650 = 0.129 m

b)

Source is moving and observer is at rest.

n’ = c n /(c-Vs) = 343 * 2650/ ( 343 – 26.1) = 2868.25 Hz

= 343/ 2868.25 = 0.119 m

c)

Source and observer are moving toward each other

n’ = ( c + Vo) n /(c-Vs) = ( 343 + 11.0)* 2650 / ( 343 – 26.1)

n’ = 2960.23 Hz

= 343/2960.23 = 0.115 m

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