A sound source producing 1.00-{\rm kHz} waves moves toward a stationary listener atone-half the speed of sound.

Question

The frequency that the listener will hear is2000 Hz.
when the source is stationary and the listener moves towardthe source at one-half the speed of sound, the frequency that thelistener hear became 1500 Hz.
Explain on physical grounds why thetwo frequencies differ.

Answer 1

I am not sure what is meant by "Explain
on physical grounds", but it can be shown mathematically why the difference
exist.