Question

An observer moves towards a stationary source of sound with a velocity equal to one-fifth of the velocity of sound. The percentage change in the frequency will be:

• A. 20%
• B. 10%
• C. 5%
• D. 0%

Answer 1

Answer: (A)

20%

Answer 2

$f' = f_0 \bigg[\frac{v-v_0}{v-v_s}\bigg]$

$⇒ f' = f_0 \bigg[ \frac{v+\frac{v}{5}}{v}\bigg]$

$⇒ f' = \frac{6f_0}{5}$

⇒ Change Percentage is $20$.

Hence, the correct option is (A): $20\%$