A source of sonic oscillations with frequency vo = 1000 Hz moves at right angles to the wall with a velocity u = 0.17 m/s. Two stationary receivers R1 and R2 are located on a straight line, coinciding with the trajectory of the source, in the following succession: R1-source-R2-wall. Which receiver registers the beatings and what is the beat frequency? The velocity of sound is equal to v = 340 m/s.