A person standing on a road transmits a sound signal to the driver...

Speed of the car, $v_c = 72 \text{ km h}^{-1} = 72 \times \dfrac{5}{18} \text{ m s}^{-1} = 20 \text{ m s}^{-1}$

Speed of sound, $v = 330 \text{ m s}^{-1}$

Original frequency, $f_0 = 1600 \text{ Hz}$

The frequency received by the car (acting as an observer moving away from the stationary source) is given by:

$f_1 = f_0 \left( \dfrac{v - v_c}{v} \right)<br><br>The car then reflects the sound, acting as a moving source moving away from the stationary person. The frequency heard by the person is:<br><br>$f_2 = f_1 \left( \dfrac{v}{v + v_c} \right)$<br><br>Substituting$f_1$into the equation for$f_2$:<br><br>$f_2 = f_0 \left( \dfrac{v - v_c}{v} \right)\left( \dfrac{v}{v + v_c} \right) = f_0 \left( \dfrac{v - v_c}{v + v_c} \right)

Substituting the given values:

$f_2 = 1600 \left( \dfrac{330 - 20}{330 + 20} \right)$

$f_2 = 1600 \left( \dfrac{310}{350} \right) = 1600 \times \dfrac{31}{35}$

$f_2 = \dfrac{49600}{35} \approx 1417.14 \text{ Hz}$

Thus, the frequency of the reflected signal heard by the person is approximately $1417 \text{ Hz}$.