Help with sound waves

[tmkgemini]

A microphone is moving in air toward a stationary source of sound (speed of sound = 343m/s). The detected frequency is 82.7Hz greater than the emitted frequency. When the microphone moves at the same speed toward the same stationary source in a liquid, the detected frequency is only 21.6Hz greater than the emitted frequency. What is the speed of sound in the liquid?


I really need help! I can't figure out this problem and I've gone all through my textbook and lecture notes!

[Andrew Mason]

A microphone is moving in air toward a stationary source of sound (speed of sound = 343m/s). The detected frequency is 82.7Hz greater than the emitted frequency. When the microphone moves at the same speed toward the same stationary source in a liquid, the detected frequency is only 21.6Hz greater than the emitted frequency. What is the speed of sound in the liquid?

This is just doppler shift. Find the speed of the microphone using the doppler formula. Then set up the equation for doppler shift in the second situation. You know the doppler shift and the relative speeds so the only unknown is the speed of sound in the liquid.

AM