SAT Subject Physics Practice Question 359: Answer and Explanation
55. The engineer of a train blows the train whistle as he approaches a crossing. A few moments later he hears an echo from the whistle. The engineer hears the echo of the whistle because of
C. constructive interference.
D. destructive interference.
E. Doppler effect.
Correct Answer: A
The correct answer is (A). An echo is the repeat sound heard when the original sound waves strike a fixed object and return toward their origin. This is the process of reflection.