12. As shown in Fig. 7, a moving point source S with speed v = 20 m/s heading toward the wall on the right generates sound wave with frequency 50 KHz. The speed of sound in air is 340 m/s. What's the beat frequency heard at D.

(A) 2.95 KHz
(B) 1.45 KHz
(C) 0.50 KHz
(D) 5.90 KHz
(E) 8.53 kHz

相關試題

相關試卷