Two identical point charges $q=+7\mathrm{.}0{10}^{-6}C$ are fixed at diagonally opposite corners of a square with sides of length $50cm.$ A test particle of charge $-3\mathrm{.}0x{10}^{-8}C,$ and mass $7\mathrm{.}0x{10}^{-8}kg,$ is released from rest at one of the empty corners of the square.

a$.$ In the given square, draw the identical point charges and the test charge. Mark their charges and distances.

b$.$ What is the electric potential at the center of the square due to the identical charges?

c$.$ What is the potential difference through which the test charge is moving?

d$.$ Using the principle of conservation of energy, determine the speed of the test charge

when it reaches the center of the square.