An ambulance is generating a siren sound at a frequency of 2,400 Hz. The speed of sound is 345.0 m/s. If the observer is traveling at a velocity of 24.00 m/s toward the stationary ambulance, then what is the frequency of the siren perceived by the observer?
A) 2,640 Hz
B) 2,567 Hz
C) 2,520 Hz
D) 2,508 Hz
E) 2,475 Hz

Question

Quizplus · Accepted Answer

The observed frequency of a moving sound source can be calculated using the formula:
observed frequency = (source frequency) x [(speed of sound ± observer's velocity) / speed of sound]
In this case, the observer is moving towards the stationary ambulance, so we use the positive sign for velocity in the formula. 
observed frequency = 2,400 Hz x [(345.0 m/s + 24.00 m/s) / 345.0 m/s]
observed frequency = 2,400 Hz x 1.0695
observed frequency = 2,567 Hz
Therefore, the observed frequency of the siren is 2,567 Hz. The correct answer is B.

An Ambulance Is Generating a Siren Sound at a Frequency