Answer:

Explanation:
From the question we are told that:
Distance of wall from CD 
Second bright fringe 
Let
Strontium vapor laser has a wavelength \lambda= 431 nm=>431 *10^{-9}m
Generally the equation for Interference is mathematically given by

Where



According to Coulomb's Law , The size of the force varies inversely as the square of the distance between the two charges. So ,if the distance between the two charges is doubled, the electrostatic force will become weak by one fourth of the original force.
After x seconds, an object will fall

where a is acceleration due to gravity and t is time
so when t=3.3
the distance it will fall is

=53.361m
it will fal 53.361 meters
A force over distance is work the unite is joules