Question

A boy yells in a narrow valley. The sound reflects off of a boulder that is 80 m away. How long will it take to hear the echo if the speed of a sound wave is 320 m/s?

(speed = )

0.25 seconds
0.50 seconds
2.0 seconds
4.0 seconds

Answer 1

Echo travels to the boulder and back: distance = 2 × 80 = 160 m.
Time = distance / speed = 160 m / 320 m/s = 0.5 s.

Answer: 0.50 seconds.