Answer:
[tex]f_{B}=12.8 Hz[/tex]
Explanation:
Let's start finding the frequency heard by the bystander due to the moving car. We need to use Doppler effect here:
[tex]f_{obs}=f_{s}\left(\frac{v}{v-v_{car}}\right)[/tex]
v is the speed of sound (v = 343 m/s)
So, we have:
[tex]f_{obs}=406\left(\frac{343}{343-10.5}\right)=418.8 Hz[/tex]
Now, the beat frequency heard by the bystander is the combine of the frequencies, it means the difference between them. Therefore the equation is given by:
[tex]f_{B}=f_{obs}-f_{s}=418.8-406=12.8 Hz[/tex]
I hope it helps you!
