Energy
The capacity to do work is called energy.It is a scalar quantity and its units are same as that of work.
The energy possessed by the virtue of motion is called kinetic energy.Consider a body of mass M and moving with velocity v, then its kinetic energy is given by
K.E = 
M
WE know that momentum (P) is given by P = Mv
Substituting in the equation K.E = M, we get
K.E = 
The energy possessed by a body due to a position or configuration is called potential energy.The potential energy is associated with mass in gravitational field, compressed spring, deformed elastic body, charged capacitor etc. The potential energy may be +ve or -ve
When the forces involved are repulsive, then potential energy is positive, eg., the potential energy of two similar charges.
2.Negative Potential Energy
When the forces involved are attractive, then potential energy is negative, eg., potential of two opposite charges.