To have a force of 3.8x10-8 the two chaarges must be 0.65m apart.
Cutting and polishing exposed rock
Answer:-81.29 J
Explanation:
Given
mass of ball 
Length of string 
height of Room 
Gravitational Potential Energy is given by

where h=distance between datum and object
here Reference is ceiling
therefore 
Potential Energy of ball w.r.t ceiling

i.e. 81.29 J of Energy is required to lift a ball of mass 2.35 kg to the ceiling