SAT Subject Physics Practice Question 427: Answer and Explanation

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Question: 427

3. A rider on a subway train hears the engineer blow the train whistle. A moment later she hears an answering whistle from an approaching train. Why does the whistle she hears from the approaching train change pitch?

A. The frequency of the waves of the approaching train's whistle is decreasing.
B. The frequency of the waves of the approaching train's whistle is increasing.
C. The loudness of the waves of the approaching train is decreasing.
D. The loudness of the waves of the approaching train is increasing.
E. The echoes of the two trains' whistles are combining.

Correct Answer: B

Explanation:

The correct answer is (B). The sound waves from the approaching whistle strike the listener's ears at an increasing rate, producing the increasing pitch.

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