A truck traveling at 74.5 kilometers per hour away from you. The driver is blowing the horn which has a frequency of 415 Hz. The speed of the sound is 346 m/s. What is the observed frequency of the sound?

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Answer 1 · 2018-01-03T12:59:10

The observed frequency is #=391.6Hz#

This is the Doppler effect

The equation is

#f_(obs)=f_s(v/(v+v_s))#

The speed of the truck is

#v_s=74.5*1000/3600=20.69ms^-1#

The frequency of the horn is

#f_s=415Hz#

The speed of sound is

#v=346ms^-1#

The frequency observed is

#f_(obs)=415*(346/(346+20.69))=391.6Hz#