An echo is returned in `3 s`. What is the distance of the reflecting surface from the source, given that the speed of sound is `342 m//s`.

Explanation

The speed of sound in air`=342"m s"^(-1)`.
Time taken by echo to return, `t=3`s
If d is the distance between the source and the reflecting surface, distance covered by sound in time `t = d + d =2d`
(distanced while going to the reflecting surface and distance d while returning back)
As distance `=` speed (of sound) `xx` time, `2d = 342("m s"^(-1) ) xx 3("s") = 1026" m"`
or `d=513` m