Physics - Sound Wave Question with Solution | TestHub

Using the Doppler effect formula for a stationary observer and a moving source approaching the observer:

$f^{\prime }=f\left(\frac{v}{v-v_s}\right)$

Substituting $f=400$ Hz, $v=340$ m/s, and $v_s=34$ m/s:

$f^{\prime }=400\left(\frac{340}{340-34}\right)$

$f^{\prime }=400\left(\frac{340}{306}\right)$

$f^{\prime }=400\left(\frac{10}{9}\right)$

$f^{\prime }=\frac{4000}{9}\approx 444.4$ Hz

The frequency heard by the observer is nearly $444$ Hz.

Answer: $444$