You are standing on the sidewalk as a police car passes you ata speed of 20 m/s.

Question

You are standing on the sidewalk as a police car passes you ata speed of 20 m/s. The car's siren has a fixed frequency of 400 Hz.At the same time a second police car is approaching you. The secondcar is going at the same speed and has an identical siren. a) what frequencies do you hear from each police car? b) what is the beat frequency if any? between the two observedfrequencies? You are standing on the sidewalk as a police car passes you ata speed of 20 m/s. The car's siren has a fixed frequency of 400 Hz.At the same time a second police car is approaching you. The secondcar is going at the same speed and has an identical siren. a) what frequencies do you hear from each police car? b) what is the beat frequency if any? between the two observedfrequencies?

Explanation / Answer

       Given that the speed ofthe police car is Vs = 20 m/s                       The frequency of the police car is f = 400 Hz              -------------------------------------------------------------------------------------     consider the police car which ispassing the observer then the frequency observed by the personat rest is                                     f1= f [ V / (V + Vs) ]                                        =400 Hz [ 343 m/s / (343 m/s - 20 m/s) ]                                         =----------- Hz    if the police car moves towards the observerthen the new frequency is                                     f2= f [ V / (V - Vs) ]                                        =400 Hz [ 343 m/s / (343 m/s - 20 m/s) ]                                         =----------- Hz     The beat frequency is f = f1 -f2 = ----------- Hz                       The frequency of the police car is f = 400 Hz              -------------------------------------------------------------------------------------     consider the police car which ispassing the observer then the frequency observed by the personat rest is                                     f1= f [ V / (V + Vs) ]                                        =400 Hz [ 343 m/s / (343 m/s - 20 m/s) ]                                         =----------- Hz                                     f1= f [ V / (V + Vs) ]                                        =400 Hz [ 343 m/s / (343 m/s - 20 m/s) ]                                         =----------- Hz    if the police car moves towards the observerthen the new frequency is                                     f2= f [ V / (V - Vs) ]                                        =400 Hz [ 343 m/s / (343 m/s - 20 m/s) ]                                         =----------- Hz     The beat frequency is f = f1 -f2 = ----------- Hz

Related Questions

Navigate

• Browse (All)
• Browse Y
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.