Question

An observer moves towards a stationary source of sound with a velocity that is one-fifth the velocity of sound. The apparent change in frequency is

• A. zero
• B. 0.05
• C. 0.2
• D. 0.001

Answer 1

Answer: (C)

0.2

Answer 2

When the observer is moving towards a stationary source
Apparent frequency $v' = v \bigg[ \frac{v + v_0}{v}\bigg]$
\hspace50mm v' = v \bigg[ \frac{v + \frac{v}{5}}{v}\bigg]
or \hspace45mm v' = \frac{6}{5} v
$\therefore$ Change in frequency $= \frac{6}{5} v - v$
\hspace50mm = \frac{1}{5} v
$\therefore$ % change = 20%