A reflector is moving with $20 \mathrm{~ms}^{-1}$ towards a stationary source of sound. If the source is…
A reflector is moving with $20 \mathrm{~ms}^{-1}$ towards a stationary source of sound. If the source is producing sound waves of $160 \mathrm{~Hz}$, then the wavelength of the reflected wave is ( speed of sound in air is $340 \mathrm{~ms}^{-1}$ )
$\frac{17}{8} \mathrm{~m}$
$\frac{17}{11} \mathrm{~m}$
$\frac{17}{9} \mathrm{~m}$
$\frac{17}{16} m$
Solution
Wavelength of the reflected wave is
$
\begin{aligned}
\lambda^{\prime} & =\left(\frac{v-v_s}{v+v_s}\right) \lambda=\left(\frac{v-v_s}{v+v_s}\right) \frac{v}{v} \\
& =\frac{340-20}{340+20} \times \frac{340}{160}=\frac{120}{360} \times \frac{340}{160} \\
\lambda^{\prime} & =\frac{17}{9} \mathrm{~m}
\end{aligned}
$