# A source of sound of frequency 256 Hz is moving rapidly towards wall with a velocity of 5m/sec. How many beats per second will be heard if sound travels at a speed of 330 m/sec?

8 years ago
Hello Student,
NOTE : If the sound reaches the observer after being reflected from a stationary surface and the medium is also stationary, the image of the source in the reflecting surface will become the source of the reflected sound.
v = v [c – v0/c – vs]
v0, vs are +ve if they are directed from source to the observer and – ve if they directed from observer to source.
v = 256 [330 – (- 5)/330 – 5] = 264 Hz
∴ Beat frequency = 264 – 256 = 8
Thanks
Rishi Sharma
2 years ago
Dear Student,

If the sound reaches the observer after being reflected from a stationary surface and the medium is also stationary,
the image of the source in the reflecting surface will become the source of the reflected sound.
v=v[c–v−o/c–vs​]
vo​, vs​ are +ve if they are directed from source to the observer and –ve if they directed from observer to source.
v=256[330–(−5)/330–5]=264Hz
∴ Beat frequency =264–256=8

Thanks and Regards