A fast train approaches a car waiting at a grade crossing and sounds its horn. A person in the car will notice that, compared to what it would be if the train were at rest, the horn sound's
A) wavelength appears to be the same.
B) wavelength appears to be longer.
C) frequency appears to be lower.
D) frequency appears to be higher.

Question

Quizplus · Accepted Answer

When the fast train approaches the car, the person in the car will perceive the frequency of the horn sound to be higher than its actual frequency. This is due to the Doppler effect, which is the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source. As the train moves towards the car, the sound waves produced by the horn are compressed, causing the frequency to increase.

A Fast Train Approaches a Car Waiting at a Grade