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

Therefore, the frequency you will hear is 696.8 Hz.

ANSWER:

696.8 Hz.