Question

NCERT CLASS IX - Science Textbook
Chapter 12 - Sound

An echo 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 - '1?

Answer 1

we know that,in the case of echo, 2d =v*t

 [ where d=distance between reflecting surface and source, v=velocity,
   t= tot.time taken ]                                                                                                                
here,t = 3s
       v = 342 m/s
hence 2d = 342*3 = 1026 m
thus, d = 1026/2= 513 m

Answer 2

time = 3 second 
v = 342 m /s 
s=v×t
s=342×3
s=1026 
we have to find the distance so total distance cover =
s+s = 1026 
2s=1026 
s=513 m