Chapter 15, Problem 5STP

To determine

To Choose:The correct option.

Answer to Problem 5STP

The answer is B- $620\text{ Hz}$ .

Explanation of Solution

Given data:

Speed of the car is $v_r=72\text{km/h}=20\text{ m/s}$ .

Frequency of the siren is $f=\text{657Hz}$ .

  $v_s=0\text{ m/s}$

Speed of sound is $v=\text{343 m/s}$ .

Formula used:

The formula used to find the frequency of the sound perceived by the driver is

$f_d=f\left(\frac{v-v_r}{v+v_s}\right)$

Calculation:

Substituting the given values, we get

  $\begin{array}{l}{\text{f}}_d=\text{657}\left(\frac{343-20}{343}\right)\\ =618.7\text{ Hz}\\ =620\text{ Hz approx}\end{array}$

Conclusion:

Hence the answer is B- $620\text{ Hz}$ .