Question

In one of the original Doppler experiments, one tuba was played on a moving flat train car at a frequency of 75 Hz, 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 approached the station at a speed of 5.0 m/s?

f(beat) = Hz

Answer 1

Answer:

1.109 Hz    

Explanation:

According to Doppler's effect, when there is relative motion between the source and the observer, an apparent frequency different from the actual one is measured.

Doppler effect:

$f'=f(\frac{v+v_o}{v-v_s})\\\Rightarrow f'=75\times (\frac{343}{343-5})=76.109Hz$

Beat frequency:

$f(beat)=f'-f\\f(beat)= 76.109-75 \\f(beat)=1.109 Hz$