The situation as shown in the figure. Here, Speed of listener,vL=1ms−1 Speed of sound,v=330ms−1 Frequency of each source, v=660Hz Apparent frequency due to P, v′=
v(v−vL)
v
Apparent frequency due to Q, v"=
v(v+vL)
v
Number of beats heard by the listener per second is v"−v′=