i am assuming the initial velocity is zero here and that 18 is the acceleration and not the velocity.
therefore you use this formula:
acceleration= (vfinal)/t [note: velocity initial is not included as it is zero, so it would just cancel out]
= 8100m/s or 8.1*10³m/s if you correct to proper sigdigs.
hope this !
if im wrong im sorry!
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.