A police car sounding a siren with a frequency of 1280 H_x is traveling at 100.0

Question

A police car sounding a siren with a frequency of 1280 H_x is traveling at 100.0 km/h. What frequencies does an observer standing next to the road hear as the car approaches and as it recedes? Enter your answers numerically separated by a comma. f_approaching f_receding = What frequencies are heard in a car traveling at 100.0 km/h in the opposite direction before and after passing the police car? Enter your answers numerically separated by a comma. f_before f_after = The police car passes a car traveling in the same direction at 80.00 km/h. What two frequencies before and after overtaking are heard in this car? Enter your answers numerically separated by a comma. f_before f_after =

Explanation / Answer

f,approach = fo*(c)/(c - v)

where fo = 1200 Hz

c = speed of sound = 340 m/s

v = 100 km/h = 100*1000/3600 = 1000/36 = 250/9 m/s

So, f,approach = 1200*(340)/(340 - 250/9)

= 1306.8 Hz <------ answer

f,receding = fo*(c)/(c + v)

= 1200*(340)/(340 + 250/9)

= 1109.4 m/s <------- answer

b)

f,before = fo*(c+v')/(c-v)

= 1200*(340 + 250/9)/(340 - 250/9)

= 1413.5 Hz <----- answer

f,after = fo*(c-v')/(c+v)

= 1200*(340 - 250/9)/(340 + 250/9)

= 1018.7 Hz <------ answer

c)

here v' = 80 km/h = 80*1000/3600 = 800/36 = 200/9 m/s

f,before =  fo*(c-v')/(c-v)

= 1200*(340 - 200/9)/(340 - 250/9)

= 1221.4 Hz

f,after = fo*(c + v')/(c + v)

= 1200*(340 + 200/9)/(340 + 250/9)

= 1181.9 Hz <------ answer

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