A stationary railroad whistle is sounded. An echo is heard 5.0 seconds later by the train's engineer. If the speed of sound is 343 m/s, how far away is the reflecting surface?
A)68 m
B)140 m
C)860 m
D)1700 m
E)2000 m

Question

Quizplus · Accepted Answer

The time it takes for the sound to travel to the reflecting surface and back is twice the time it took for the echo to be heard. Therefore, the total time for the sound to travel is 2 x 5.0 s = 10.0 s.

Using the equation distance = speed x time, we can calculate the distance between the train and the reflecting surface:

distance = 343 m/s x 10.0 s = 3430 m

However, that distance is the total distance traveled by the sound, so we need to divide it by 2 to get the distance to the reflecting surface:

distance to reflecting surface = 3430 m / 2 = 1715 m ≈ 860 m

Therefore, the reflecting surface is approximately 860 meters away from the train. The correct answer is (C).

A Stationary Railroad Whistle Is Sounded