Question

a boy receives his echo 3 sec later. Find the distance of the reflecting surface from the boy. Speed of sound in is 342m/s

Answer 1

Distanct=speed*time
Distance= 2x
Speed= 342
Time=3 seconds
2x=342*3
X= 513m

Answer 2

Echo is received after 3 sec.
It means light travelled 1.5 sec to the reflecting surface and 1.5 sec from the reflecting surface to the boy.
Distance travelled in 1.5 sec = 342m * 1.5
=513m