Physics - Sound Wave Question with Solution | TestHub

The reflection sound appears to propagate in a direction opposite to that of moving engine. Thus, the source and the observer can be presumed to approach each other with same velocity.

${\mathrm{v}}^{\mathrm{\prime }}=\frac{\mathrm{v}\left(\mathrm{v}+{\mathrm{v}}_{\mathrm{o}}\right)}{\left(\mathrm{v}-{\mathrm{v}}_{\mathrm{s}}\right)}$

$=\mathrm{v}\left(\frac{\mathrm{v}+{\mathrm{v}}_{\mathrm{s}}}{\mathrm{v}-{\mathrm{v}}_{\mathrm{s}}}\right) \left(\because {\mathrm{v}}_{\mathrm{o}}={\mathrm{v}}_{\mathrm{s}}\right)$

$⟹{\mathrm{v}}^{\mathrm{\prime }}=1.2\left(\frac{350+50}{350-50}\right)$

$=\frac{1.2\times 400}{300}=1.6\mathrm{ }\mathrm{kHz}$