Two automobiles are equipped with the same single-frequency horn. When one is at rest and the other is moving toward the first at 10 m/s, the driver at rest hears a beat frequency of 5.0 Hz.

What is the frequency the horns emit?

f = 4.85 Hz

Explanation:

This question is an example of the Doppler's effect

We are given that;

The source velocity; v_s = 10 m/s

The apparent frequency f' = 5 Hz

We will also need the speed of sound in air and it has a constant value of 340 m/s. Thus, v = 340 m/s

Now, the true frequency is given by the formula;

f = [ (v - v_s) / v]•f'

Where;

v is speed of sound in air

v_s is speed of source

f' is apparent frequency

Thus, plugging in the relevant values, we have;

f = [ (340 - 10) / 340]•5

f = (330/340) •5

f = 4.85 Hz