In one of the original Doppler experiments, a tuba was played at a frequency of 53.0 Hz on a moving flat train car, and a second identical tuba played the same tone while at rest in the railway station.

What beat frequency was heard in the station if the train car approached the station at a speed of 19.0 m/s

The source is at rest, and the train which is an observer is moving toward the source. Therefore, according to the Doppler effect, we have: f\\' = f ( 1 + v₀/v) = 75 (1 + 10/343) = 77.2 Hz \ \ The beat frequency is the difference between those two above frequencies: f_beat = 77.2 - 75 = 2.2 Hz

The source frequency is

The speed of the train car approaching the station is

Doppler effect: Frequency observed of the train car approaching towards the stationary is .

Here is the frequency of the sound heard by the listener.

is the velocity of the listener.

is the velocity of the source and

is the frequency of the sound emitted by the souce.

The beat frequency is the difference between those two frequencies:

Beat frequency is