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`.