A bat is flitting about in a cave, navigating via ultrasonic beeps. Assume that the sound emission frequency of the bat is 40 kHz. During one fast swoop directly toward a flat wall surface, the bat is moving at 0.03 times the speed of sound in air. What frequency does the bat hear reflected off the wall?

Ultrasonic beep frequency emitted by the bat, ν=40 kHz 
Velocity of the bat, vb=0.03v
where, v=velocity of sound in air 
The apparent frequency of the sound striking the wall is given as:
This frequency is reflected by the stationary wall vs=0 towards the bat.
The frequency ν'' of the sound received by the bat: