Bats find insects by sending out pulses of ultrasound and detecting the echoes.
A bat sends out a pulse of ultrasound with a frequency of 40 kHz40\ \text{kHz}40 kHz.
The speed of sound in air is 340 m/s.
Calculate the wavelength of the ultrasound.
The echo from a moth returns to the bat 0.020 s after the pulse is sent.
Calculate the distance between the bat and the moth.
Explain why a person standing near the bat cannot hear the pulse.