The speed of sound at 22 degrees Celsius is v = 344.31 m/s.
The pitch, p, and frequency, f are related as
[tex]\text{p }\propto f[/tex]If pitch increases, then frequency increases, and if pitch decreases the frequency decreases.
The pitch decreased by 10%, so the frequency also decreases by 10%.
Let the original frequency be f.
The observed frequency will be
[tex]\begin{gathered} f^{\prime}=f-\frac{10f}{100} \\ =\text{ }\frac{9f}{10} \end{gathered}[/tex]Let the speed of the car be v' which can be calculated by the formula
[tex]\begin{gathered} f^{\prime}=(\frac{v}{v+v^{\prime}})f \\ v^{\prime}=(\frac{f}{f^{\prime}}-1)v \end{gathered}[/tex]Substituting the values, the speed of the car will be
[tex]\begin{gathered} v^{\prime}=(\frac{f}{\frac{9}{10}f}-1)\times344.31 \\ =38.25m/s^2 \end{gathered}[/tex]
