A source of sound \(A\) emitting waves of frequency \(1800\,Hz\) is falling towards ground with a terminal speed \(v.\) The observer \(B\) on the ground directly beneath the source receives waves of frequency \(2150\,Hz.\) The source \(A\) receives waves, reflected from ground of frequency nearly ..... \(Hz\) (Speed of sound \(= 343\,m/s\) )

\({v_{t}=v}\)

\({f_{B}=2150 \mathrm{Hz}}\)

Reflected wave frequency received by \(A.\)

\(f_{A}^{\prime}=?\)

Applying doppler's effect of sound,

\(f^{\prime}=\frac{v_{s} f}{v_{s}-v_{t}}\)

Here, \(v_{t}=v_{s}\left(1-\frac{f_{A}}{f_{B}}\right)=343\left(1-\frac{1800}{2150}\right)\)

\(v_{t}=55.8372 \mathrm{m} / \mathrm{s}\)

Now, for the reflected wave,

\(\therefore \mathrm{f}_{\mathrm{A}}^{\prime}=\left(\frac{\mathrm{v}_{\mathrm{s}}+\mathrm{v}_{\mathrm{t}}}{\mathrm{v}_{\mathrm{s}}-\mathrm{v}_{\mathrm{t}}}\right) \mathrm{f}_{\mathrm{A}}\)

\(=\left(\begin{array}{l}{343+55.83} \\ {343-55.83}\end{array}\right) \times 1800\)

\(=2499.44 \approx 2500 \mathrm{Hz}\)