A source of sonic oscillations with frequency `v_(0)=100Hz` moves at right angles to the wall with a velocity `u=0.17 m//s`. Two stationary receivers `R_(1)` and `R_(2)` are located on a straight line, coinciding with the trajectory of the source , in the following succession :` R_(1)-` source `-R_(2)-` wall. Which receiver registers the beatings and what is the beat frequency ? The velocity of sound is equal to `upsilon= 340 m//s`.

Explanation

`R_2` is approached by the source and the image source at the same speed so `R_2` receives waves of the same frequency and hence, it does not register beats. `R_1` is approached by the image source while the source itself recedes from it Hence it it receives waves of different wavelength so it registers beats.
`N_1`(apparent frequency of the source wave)
`=(340-0)/(340-(0.17))xx1000=1000.5Hz`
`N_2`(apparent frequency of the reflected wave)
`=(340-0)/(340+0.17)xx1000=999.5Hz`
Therefore beats registered`=1000.5-999.5=1.0Hz`