Question

A police car is moving at a speed of 20.0 mi/h, its siren emits a sinusoidal wave with frequency 5.00×102 Hz to alert Regina Transit bus of a trafic violation. The air temperature is 24.0◦C. a) What is the overall change in frequency heard by the passanger waiting for the bus in the bus stop as the police car aproaches, and moves away from the passanger ? b) What is the wavelength detected by the passenger waiting for the bus as the police car moves away from him?

Answer 1

According to Doppler Equation,

Observed Frequency,  

Here Observer is at rest . Observer frequency,    ...... Eqn (1)

First we have to determine the velocity of sound at , which is given by,

where, Adiabatic Index for air , Gas constant for air,

Temperature,  

and given actual frequency,

a)

Case i ) Police car moving towards the bus stop

Here, The source moving towards the bus stop,  

Substituting on Eqn (1) ............

Change in frequency,   

Case ii ) Police car moving away the bus stop

Here, The source moving towards the bus stop,  

Substituting on Eqn (1) ............

Change in frequency,

b)  

Frequency of sound when police car moves moves away from passeneger,  

Bur Velocity,   Or Wavelength,

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