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162 A train approaches a crossing and continuously blows its horn.  Compared to the sound of the engineer, the sound heard by the driver of a car waiting at the crossing has
   
A. higher pitch and shorter wavelength                1
f ' = --------------- f
                   vs
        (1  -   ----- )
                    v

      
The above equation for the frequency of sound when the source is approaching the observer.

The denominator will have a value less than one.  This means the observer will hear a higher pitch due to a shorter wavelength.

B. higher pitch and longer wavelength
C. lower pitch and shorter wavelength
D. lower pitch and longer wavelength