Question

You are driving at 20 m/s. A police car is coming toward you from theopposite direction at 30 m/s. The police siren is emitted at 600 Hz. Whatwill be the frequency you hear?After you pass the police car, what will be the frequency you hear?

Answer 1

Given:

My speed = 20 m/s

Speed of car 2 = 30 m/s

Frequency of police car = 600 Hz.

Let's find the frequency I hear.

Apply Doppler equation since the source and observer are towrads each other

$Fa=(\frac{V+V_o}{V-V_s})F_o$

Where:

V is the speed of sound = 340 m/s.

Vo is the speed of the observer(my speed) = 20 m/s

Vs is the speed of source(speed of police car) = 30 m/s

Fo = 600 Hz.

Thus, we have:

$\begin{gathered} Fa=(\frac{340+20}{340-30})600 \\ \\ Fa=(\frac{360}{310})600 \\ \\ Fa=696.8\text{ Hz} \end{gathered}$

Therefore, the frequency you will hear is 696.8 Hz.

ANSWER:

696.8 Hz.