To solve this problem, we need to understand the concept of the Doppler Effect in physics, which describes how the frequency of a sound wave changes due to the relative motion between the source of the sound and the observer.

Concept of Doppler Effect

The Doppler Effect occurs when there is a relative motion between a sound source and an observer. It affects the frequency of the sound perceived by the observer. The formula for the Doppler Effect when the source and observer are in motion is:

f' = f \frac{(v + v_o)}{(v - v_s)}

• f' is the observed frequency.
• f is the emitted frequency (frequency of the horn sound).
• v is the speed of sound in air.
• v_o is the velocity of the observer relative to the medium (positive if the observer is moving towards the source).
• v_s is the velocity of the source relative to the medium (positive if the source is moving away from the observer).

Analyzing the Situation

In this problem:

• The car is at rest, so v_s = 0.
• The person is walking towards the car, so v_o > 0.

Substituting these values into the Doppler Effect formula gives:

f' = f \frac{(v + v_o)}{v}

Since v_o > 0, the term (v + v_o) > v, which implies that f' > f. This means the observed frequency f' is greater than the actual frequency f, indicating that the frequency of the sound increases.

Conclusion

Thus, the frequency of the sound heard by the person increases as they walk towards the car.

Correct Answer: The frequency increases