A flying bat emits squeaks at a frequency of 80 MHz, if a stationary observer picks up the frequency of the squeaks as 78 MHz, is the bat moving towards or away from the listener? Determine the speed of the bat.

Answer 1

Fb = 80 kHz = Freq. emitted by the bat.
Fh = 78 kHz = Freq. heard.
Vs = 343 m/s = Velocity of sound in air.

a. The bat is moving away.

b. Fh = (Vs-Vr)/(Vs+Vb) * Fb = 78 kHz
(343-0)/(343+Vb) * 80 = 78
Solve for Vb, the velocity of the bat.