Question

a)What frequency is received by a person watching an oncoming ambulance moving at 120 km/h and emitting a steady 700 Hz sound from its siren? The speed of sound on this day is 345 m/s.

b)What frequency does she receive after the ambulance has passed?
Vo=120km/h = 120,000m/3600s = 33.33 m/s.

a. Fr = ((Vs+Vr)/(Vs-Vo))*Fo
Fr=(345+0)/(345-33.33)*700Hz = 774.9 Hz

b. Fr = ((345-0)/(345+33.33))*700=356 Hz
= Freq. heard by the receiver(person).

CORRECTION:

b. Fr = 638.33 Hz.

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