the echo of a sound is heard 2 seconds after the sound from a cracker is produced. how far away is the reflector ( cliffs ) from the listener ? take velocity of sound as 340 m/s.

@Shagun,

We will use the following simple relation,

distance travelled by the sound = speed of sound X time taken

d = s X t

here

s = 340 m/s

t = 2 s

thus, the total distance is

D = 340 X 2  = 680 m

as the sound reflects back along the same path, the distance to the hill will be 

half of the total distance travelled by the sound wave.

So,

d = 680/2 = 340 m.