A friend of yours is loudly singing a single note at 400 Hz while racing toward you at 25.0 m/s on a day when the speed of sound is 340 m/s.a. What frequency do you hear?

(II) A bat at rest sends out ultrasonic sound waves at 50.0 kHz and receives them returned from an object moving directly away from it at 22.0 m/s. What is the received sound frequency?

A fish finder uses a sonar device that sends 20,000-Hz sound pulses downward from the bottom of the boat, and then detects echoes. If the maximum depth for which it is designed to work is 85 m, what is the minimum time between pulses (in fresh water)?

(II) Two trains emit 508-Hz whistles. One train is stationary. The conductor on the stationary train hears a 4.5-Hz beat frequency when the other train approaches. What is the speed of the moving train?1