The siren on an ambulance is emitting a sound whose frequency is 2550 Hz . The s

Question

The siren on an ambulance is emitting a sound whose frequency is 2550 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 26.4 m/s. Determine the wavelength and the frequency of the sound you hear. (c) If the ambulance is moving toward you at a speed of26.4 m/s and you are moving toward it at a speed of 15.0 m/s, find the wavelength and frequency of the sound you hear.

Explanation / Answer

In classical physics, where the speeds of source and the receiver relative to the medium are lower than thevelocity of waves in the medium, the relationship between observed frequency f and emitted frequency fo is given by:
f = [(V+Vr)/(V+Vs)] x fo
Where
V is the velocity of waves in the medium
Vr is the velocity of the receiver relative to the medium; positive if the receiver is moving towards the source.
Vs is the velocity of the source relative to the medium; positive if the source is moving away from the receiver.
The frequency is decreased if either is moving away from the other.

iam considering lambda - L

(a) By v = nL
=>L = 343/2550 = 0.1345 m
& n = 2550 Hz

(b) f = [(V+Vr)/(V+Vs)] x fo
=>f = [343/(343 - 26.4] x 2550
=>f = 2762.63 Hz

(c) f = [(V+Vr)/(V+Vs)] x fo
=>f = [(343+15)/(343 - 26.4)] x 2550
=>f = 2883.45Hz

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