you are standing on thesidewalk as a police car recedes from you at a speed of 2

Question

you are standing on thesidewalk as a police car recedes from you at a speed of 20m/s. Thecar's siren has a fixed frequency of 400 hz. At the same time asecond police car approaching you. The second is going at the samespeed and has an identical siren. a) what frequencies do you hear from each police car? b) what is the frequency difference, if any, between the twoobserved frequencies. you are standing on thesidewalk as a police car recedes from you at a speed of 20m/s. Thecar's siren has a fixed frequency of 400 hz. At the same time asecond police car approaching you. The second is going at the samespeed and has an identical siren. a) what frequencies do you hear from each police car? b) what is the frequency difference, if any, between the twoobserved frequencies. a) what frequencies do you hear from each police car? b) what is the frequency difference, if any, between the twoobserved frequencies.

Explanation / Answer

use the doppler effect equation f(heard)=[(v+vr)/(v+vs)]*f(real) a) v=343m/s (speed of sound) from the car going away from you, you hear f=[(343+0)/(343+20)]*400 f=377.96Hz from the car coming towards you, you hear f=[(343+0)/(343-20)]*400 f=424.77Hz b) the freq difference = (424.77Hz-377.96Hz) =46.81Hz

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