Question

A source of sound of frequency n and a listener approach each other with a velocity equal to $\frac{1}{20}$ of velocity of sound. The apparent frequency heard by the listener is

• A. $\left(\frac{21}{19}\right)n$
• B. $\left(\frac{20}{21}\right)n$
• C. $\left(\frac{21}{20}\right)n$
• D. $\left(\frac{19}{20}\right)n$

Answer 1

The correct option is A $\left(\frac{21}{19}\right)n$

When both the source and listener are moving towards each other
Apparent frequency, n' $=n\left(\frac{v+v_0}{v-v_s}\right)$
$=n\left(\frac{v+\frac{1}{20}v}{v-\frac{1}{20}v}\right)=\frac{21}{19}n$