Question

A source of sound of frequency 256 Hz is moving towards a wall with a velocity of 5 m/s. How many beats per second will be heard by an observer O standing in such a positoin that the source S is between O and wall? `(c=330(m)/(s)`)

Answer 1

Correct Answer - `7.87 Hz`
Frequency reaching the wall `f_(1)=f_(0)((v)/(v-v_(s)))`
Frequency received by the observer
`f_(1)=f_(1),((v+v_(s))/(v))=f_(0)((v+v_(s))/(v-v_(s)))`
`:.` Beat frequency
`Delta f=f_(0)((v+v_(s))/(v-v_(s)))-f_(0)=256((330+5)/(330-5))-256`
`=7.87 Hz`