A source of sound A emitting waves of frequency 1800 ~Hz is falling...

Given $\mathrm{f}_{\mathrm{A}}=1800 \mathrm{~Hz}$$\begin{aligned}&\mathrm{v}_{\mathrm{t}}=\mathrm{v}\\ &\mathrm{f}_{\mathrm{B}}=2150 \mathrm{~Hz} \end{aligned}$Reflected wave frequency received by $\mathrm{A}$, $\mathrm{f}_{\mathrm{A}}{ }^{\prime}=$ ? Applying doppler's effect of sound, $\mathrmf^{\prime}=\frac{\mathrm{v}_{\mathrm{s}} \mathrm{f}}{\mathrm{v}_{\mathrm{s}}-\mathrm{v}_{\mathrm{t}}}$ Here, $\mathrm{v}_{\mathrm{t}}=\mathrm{v}_{\mathrm{s}}\left(1-\frac{\mathrm{f}_{\mathrm{A}}}{\mathrm{f}_{\mathrm{B}}}\right)=343\left(1-\frac{1800}{2150}\right)\mathrm{v}_{\mathrm{t}}=55.8372 \mathrm{~m} / \mathrm{s}$ Now, for the reflected wave,\begin{aligned}&\therefore \mathrm{f}_{\mathrm{A}}{ }^{\prime}=\left(\frac{\mathrm{v}_{\mathrm{s}}+\mathrm{v}_{\mathrm{t}}}{\mathrm{v}_{\mathrm{s}}-\mathrm{v}_{\mathrm{t}}}\right) \mathrm{f}_{\mathrm{A}}\\ &=\left(\frac{343+55.83}{343-55.83}\right) \times1800 \\ &=2499.44 \approx2500 \mathrm{~Hz} \end{aligned}$$