Physics - Sound Wave Question with Solution | TestHub

Aparent pitch heard by the observer ${\mathrm{f}}^{\prime }=\frac{4}{5}\mathrm{f}$ where, $f$ is the original pitch of the engine. As the apparent frequency is lowered, thus the engine must be moving away from the stationary observer. From Doppler effect, apparent frequency heard: $\begin{array}{rl}& {\mathrm{f}}^{\prime }=\mathrm{f}\left[\frac{{\mathrm{V}}_{\text{sound }}}{{\mathrm{V}}_{\text{sound }}+{\mathrm{V}}_{\text{source }}}\right]\\ & \therefore \frac{4\mathrm{f}}{5}=\left[\frac{350}{350+{\mathrm{V}}_{\text{Source }}}\right]\\ & \Rightarrow {\mathrm{V}}_{\text{Source }}=87.5\end{array}$