Explanation:
Echoes occur due to the reflection of sound from any obstacle, but not all the reflected sound waves lead to the phenomenon of echo. For the echo to be heard it actually depends upon the human perception as well, human ears can encounter the difference between the sound wave directly form the source and the reflected sound waves only if there is a minimum time gap of one-tenth of a second. For this time gap in the atmosphere at normal temperature and pressure the obstacle must be at least 7 meters away from the sound source.
Answer:
They will meet at a distance of 7.57 m
Given:
Initial velocity of policeman in the x- direction, 
The distance between the buildings, 
The building is lower by a height, h = 2.5 m
Solution:
Now,
When the policeman jumps from a height of 2.5 m, then his initial velocity, u was 0.
Thus
From the second eqn of motion, we can write:


t = 0.707 s
Now,
When the policeman was chasing across:


The distance they will meet at:
9.57 - 2.0 = 7.57 m
51.448 g is the required answer!