A bat flies toward a wall, emitting a steady sound with a frequency of 25.0 kHz. This bat hears its own sound plus the sound reflected by the wall.
How fast should the bat fly, v_b, to hear a beat frequency of 220 Hz?
Take the speed of sound to be 344 m/s.
f_beat = f_a - f_b
The Attempt at a Solution
I let the speed of sound be v and let the emitted frequency be f_e and got an expression for the beat frequency:
f_beat = ((v+v_b)/(v-v_b)-1)f_e
Didn't get the right answer... Doing it another way I got
f_beat = (v^2/(v-v_b)^2 - 1)f_e