Chapter 10, Problem 40R

To determine

which will occur from the flagger’s perspective among the options such as (A) the sound’s speed will decrease as the car passes (B) the sound’s speed will increase as the car passes (C) the sound’s frequency will decrease as the car passes (D) the sound’s frequency will increase as the car passes.

Answer to Problem 40R

The correct option is (C).

Explanation of Solution

Introduction:

Given, in the figure a car passes a flagger. In this case, the car is the source of sound and the flagger is the receiver of sound. As the car passes, the frequency decreases from the flagger’s perspective.

A shift in frequency occurs in the sound wave as the source or receiver is moving. This is called the Doppler Effect. As the car approaches the listener, in this case the flagger, the sound waves get close together and the frequency increases. As the car speeds away from the flagger the sound wave moves apart, decreasing the frequency.

Conclusion:

Hence, the correct answer is the sound’s frequency will decrease as the car passes.