Question

An echo was heard after 3 seconds. what is the distance of the reflecting surface from the source, given that the speed of sound is 342 m/s?

Answer 1

Speed of sound,
                           V = 342 m/s

Time taken for listening the echo,
                                                       t = 3 s

Distance travelled by the sound 
                                        
                                 ⇒ V x t
                                ⇒ 342 m/s x 3 s
                              ⇒ 1026 m  

In 3 s sound has to travel twice the distance between the reflecting surface and the person.
 Therefore the distance between the reflecting surface and the person
                                          = 1026 m / 2
                                          = 513 m 


Hope it helps :)

Answer 2

Given , speed of sound = 342 m/s
Time taken for the echo to be heard = 3 seconds
 2 x Distance traveled by echo = distance of reflecting from the source
Distance = speed x time
                =   342 x 3 = 1026 m
======================================================

But echo travels twice the distance between the reflecting surface and the source.
So, the distance between reflecting surface and the source = 1026/2 = 513 m