Four identical point charges (+6.0 nC) are placed at the corners of a rectangle which measures 6.0 m×8.0 m. If the electric potential is taken to be zero at infinity, what is the potential at the geometric center of this rectangle

When the displacement of a mass on a spring is 12a the half of the amplitude, what fraction of the mechanical energy is kinetic energy? at what displacement, as a fraction of a, is the mechanical energy half kinetic and half potential?