A train approaches a vertical cliff with a speed of while sounding its whistle of…

PHYSICS · Subjective · AP · Physics 2: Algebra-based · Waves Sound and Physical Optics · Waves Sound and Physical Optics

Problem

A train approaches a vertical cliff with a speed of

20\,\text{m\,s}^{-1}

while sounding its whistle of frequency

400\,\text{Hz}

. The speed of sound in air is

340\,\text{m\,s}^{-1}

. After reflection from the cliff, the driver hears beats between the original sound and the echo. Calculate the beat frequency heard.