Question

The velocity of a listener who is moving away from a stationary source of sound such that the listener notices 5% apparent decrease in frequency of sound is

(Velocity of sound in air =340 m/s)

• A. 12.5 ms${}^{-1}$
• B. 17 ms${}^{-1}$
• C. 25 ms${}^{-1}$
• D. 34 ms${}^{-1}$

Answer 1

Answer: (B)

17 ms${}^{-1}$

Given :$\frac{{\delta }^1}{\delta }=\frac{95}{100}$
$V=340m/s$

By Doppler effect formula:
${\delta }^1=\delta \left(\frac{V-V_0}{V-V_s}\right)$
$\frac{{\delta }^1}{\delta }=\left(\frac{340-V}{340-0}\right)$
$\frac{95}{100}=\frac{340-V}{340}$
$340\times 95=340\times 100-100V$
$100V=340\times 5$
$V=\frac{340\times 5}{100}$$=17m/s$