$A$ girl is sitting in the middle of a park of dimension $12 \,m \times 12 \,m$. On the left side of it there is a building adjoining the park and on the right side of the park,there is a road adjoining the park. $A$ sound is produced on the road by a cracker. Is it possible for the girl to hear the echo of this sound? Explain your answer.

(D) To hear an echo,the time interval between the original sound and the reflected sound must be at least $0.1 \,s$.
The minimum distance required for the reflected sound wave to be heard as an echo is calculated as:
Distance = Velocity of sound $\times$ Time interval
Distance = $344 \,m/s \times 0.1 \,s = 34.4 \,m$.
In this scenario,the girl is in the middle of a $12 \,m$ wide park. The sound travels from the road to the building $(6 \,m)$ and reflects back to the girl $(6 \,m)$.
Total distance travelled by the reflected sound = $6 \,m + 6 \,m = 12 \,m$.
Since $12 \,m < 34.4 \,m$,the reflected sound reaches the girl in less than $0.1 \,s$. Therefore,the girl cannot hear a distinct echo.