Obtain an expression for the apparent frequency of sound for an observer moving towards `//` away from a stationary source of sound.

Explanation

Let v be the velocity of sound in still air. Let `v_(0)` be the velocity of an observer.
Let `T_(0)` be the time associated with observer in moving from 0 to 0.
`t_(n+1) - t_(1)= nT_(0)-(nv_(0)T_(0))/( v_(0) +v) = nT_(0)[ (v_(0) + v- v_(0))/(v_(0) + v)]`
i.e., `( t_(n+1)-t_(1)) =(nT_(0) v)/( v+ v(0))`

Apparent frequency of sound as heard by the observer
`f =( 1)/( T ) = ( v+ v_(0))/( T_(0)v)`
i.e., `f= f_(0)"" (v+ v_(0))/(v)`
Apparent wavelength `lambda = lambda_(0)`
For an observer moving away from the source.
`f = f_(0) ""(v-v_(0))/(v) ` and `Delta lambda = 0`