Answer: A person leaning over a 125-m-deep well

Solution 73P

For the sound coming directly to the observer at the top of the well,the source is moving away from the listener.for the reflected sound,the water at the bottom of the well is the listener so the source is moving toward the listener.the water reflect same frequency sound receives.    

Here the velocity is needed to calculate frequency that is calculated by using equation

Where, depth of well

            Acceleration due to gravity

            Siren emitting sound of frequency

Then,  

               v ~  

(a).The frequency and wavelength of the sound the person hears (a) coming directly from the siren

Frequency