Question

What is the quality of the sound of an ambulance's siren when it moves toward a stationary hearer? What is the quality of the sound of an ambulance's siren when it moves away from a stationary hearer?

Answer 1

Answer:

a. The quality of the sound would have a high pitch and thus be loud.

b. The quality of the sound would have a low pitch and thus would have a lower volume than the sound from the source.

Explanation:

Using the formula for Doppler shift f' = (v ± v')f/(v ± v") where v = speed of sound in air, v'= speed of hearer = 0 m/s (since he is stationary), v" = speed of ambulance and f = frequency of sound from ambulance

So, f' = (v ± v')f/(v ± v")

f' = (v ± 0)f/(v ± v")

f' = vf/(v ± v")

a. What is the quality of the sound of an ambulance's siren when it moves toward a stationary hearer?

Since the source (ambulance) moves towards the detector, (hearer), we would get an upwards shift in frequency. (Since our denominator has to be a minimum, so we use the minus sign for v"). So, the quality of the sound would have a high pitch and thus be loud.

b. What is the quality of the sound of an ambulance's siren when it moves away from a stationary hearer?

Since the source (ambulance) moves away the detector, (hearer), we would get a downward shift in frequency. (Since our denominator has to be a maximum, so we use the plus sign for v"). So, the quality of the sound would have a low pitch and thus would have a lower volume than the sound from the source.

Answer 2

Answer:

A) As the ambulance's siren moves toward a stationary hearer, the quality of sound will have a higher pitch

B) As the ambulance's siren moves away from a stationary hearer, the quality of sound will have a lower pitch.

Explanation:

From Doppler effect, the closer the source of sound gets to the observer, the higher the frequency and in turn the higher the pitch.

Meanwhile, the farther a source goes from an observer, the lower the frequency of the sound and also the lower the pitch.

Thus, as the ambulance's siren moves toward a stationary hearer, the quality of sound will have a higher pitch.

As the ambulance's siren moves away from a stationary hearer, the quality of sound will have a lower pitch.