Question

A stationary sound source S of frequency 334 Hz and a stationary observer O are placed near reflecting surface moving away from the source with velocity 2m/s as shown in figure. Velocity of sound waves in air v = 330 m/s. The apparent frequency of echo is –

• A. 332 Hz
• B. 326 Hz
• C. 334 Hz
• D. 330 Hz

Answer 1

Answer: (D)

330 Hz

Answer 2

F_echo = f_ac $\left\lbrack \frac{V–V_{0}}{V + V_{S}} \right\rbrack$ = 334 $\left\lbrack \frac{330–2}{330 + 2} \right\rbrack$

= 334 × $\frac{328}{332}$ = 330 Hz