Subject :NSO Class : Class 8
Read the given passage and select the correct option for the following questions. The sound returning back towards the source after suffering reflection from a distant obstacle like wall, hill etc. is called an echo. A cracker is fired by a child. The child hears an echo from a cliff 4 seconds after the sound produced by a cracker. The speed of sound in air at 20°C is 344 m s-1.
What is the minimum distance between the observer and the obstacle for echo to be heard?
A17.2 m
B15.2 m
C14.2 m
D34.4 m