Chapter 10, Problem 43R

To determine

To explain: how a train is moving when a car comes to a railroad crossing, the driver hears a train’s whistle and the pitch becomes lower.

Explanation of Solution

Introduction:

The movement of the train can be assumed from the Doppler Effect. The train is moving away from the rail road crossing.

According to the Doppler Effect, the frequency of sound wave decreases as the distance between the source and the receiver increases. As given in the question, the driver hears the train’s whistle and its pitch lowers, it can be assumed that the pitch of the whistle lowers as the car stops at the rail road crossing and the train moves away from the crossing.

Conclusion:

Thus, it can be concluded that the train is moving away from the railroad crossing.