Question

Source of sound of frequency 256 Hz is moving rapidly towards a wall with a velocity of 5m/s. The speed of sound is 330 m/s. If the observer is between the wall and the source, then beats per second heard will be

• A. 7.8 Hz
• B. 7.7 Hz
• C. 3.9 Hz
• D. Zero

Answer 1

The correct option is D Zero

The observer will hear two sound, one directly from source and other from reflected image of sound


Hence number of beats heard per second

$=\left(\frac{v}{v-v_s}\right)n-\left(\frac{v}{v-v_s}\right)n$
$=0$