Conservation of energy...
As the electron is released (i.e. has zero velocity) it obtains a charge energy, which is fully turned to kinetic energy the very moment that it crosses the center of the hole. Equate the two energies.
An infinite dielectric sheet having charge density has a hole of radius in it. An electron is released on the axis of the hole at a distance from the centre. Find the speed with which it crosses the plane of the sheet.
How to do it?