Question 20N.2.HL.TZ0.4d(ii)

Two loudspeakers, A and B, are driven in phase and with the same amplitude at a frequency of $850 \mathrm{Hz}$. Point P is located $22.5 \mathrm{m}$ from A and $24.3 \mathrm{m}$ from B. The speed of sound is $340 \mathrm{m} {\mathrm{s}}^{-1}$.

In another experiment, loudspeaker A is stationary and emits sound with a frequency of $850 \mathrm{Hz}$. The microphone is moving directly away from the loudspeaker with a constant speed $v$. The frequency of sound recorded by the microphone is $845 \mathrm{Hz}$.