AP Physics 1 Question 459: Answer and Explanation
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7. As a train approaches the next stop, the conductor blows the horn and applies the brakes on the train. What will a person standing at the train stop hear as the train approaches?
- A. A decrease in the frequency and an increase in the intensity of the horn
- B. An increase in the frequency and a decrease in the intensity of the horn
- C. A decrease in both the frequency and intensity of the horn
- D. An increase in both the frequency and intensity of the horn
Correct Answer: A
As the train approaches the person, the person perceives the sound of the horn with a frequency higher than the original frequency emitted from the train due to the Doppler effect. As the train slows, the person still perceives a higher frequency but it is not as high as when the train was traveling faster. As a result, the person hears a decrease in the frequency of the horn. As the train approaches, the distance between the person and the train decreases. This leads to an increase in the intensity of the horn perceived by the person.