An ambulance is generating a siren sound at a frequency of 2,000 Hz. The speed of sound is 345.0 m/s. The observer and the ambulance are traveling toward each other at a velocity of 24.00 m/s. If the observer is stationary, what is the frequency of the siren perceived by the observer?
A) 2,032 Hz
B) 2,150 Hz
C) 2,220 Hz
D) 2,575 Hz
E) 2,750 Hz

Question

Quizplus · Accepted Answer

First, we need to use the formula for the frequency of sound heard by a stationary observer when a sound source is moving towards or away from the observer:
f' = f((v + V) / (v ± Vs))
where
f = frequency emitted by the source (2,000 Hz in this case)
v = velocity of sound in air (345 m/s)
V = velocity of the observer (24.00 m/s since the observer and ambulance are traveling towards each other)
Vs = velocity of the source (ambulance) (assumed to be zero since it is not given)

Plugging in the values, we get:
f' = 2,000 ((345+24) / (345 - 0))
f' = 2,000 (369 / 345)
f' = 2,150 Hz

Therefore, the frequency of the siren perceived by the observer is 2,150 Hz (choice B).

An Ambulance Is Generating a Siren Sound at a Frequency