Kf stands for final kinetic energy, which is the total energy possessed by an object due to its motion after a collision or interaction has occurred.
In physics, work refers to transferring energy to or from an object by applying a force over a distance.
Kinetic energy is the energy possessed by an object due to its motion and is directly proportional to its mass and the square of its velocity.
Mechanical energy refers to the sum of an object's potential energy and kinetic energy.