Work Energy and Power Test - 5

According to work energy theorem :

Net work done on a body equals change in its kinetic energy

So it does not give any information about time dependence. 

Potential energy is the stored energy of an object. It is the energy by virtue of an object's position relative to other objects. Potential energy is often associated with restoring forces such as a spring or the force of gravity. It is applicable only for conservative forces.

A force is said to be conservative if work done by this force is independent of path and is dependent only on end points .

Mechanical energy is the sum of kinetic and potential energy in an object that is used to do work. In other words, it is energy in an object due to its motion or position, or both. In case of conservative forces total mechanical energy remains conserved because potential energy applicable only for conservative forces.

mechanical energy = sum of potential and kinetic energies

a falling ball will have both these energies in between topmost and bottomost points of its motion so mechanical energy is the sum of potential and kinetic energies.

Mass–Energy equivalence states that anything having mass has an equivalent amount of energy and vice versa, with these fundamental quantities directly relating to one another by Einstein's theory of special relativity. It shows that matter (as mass) and energy can be converted into each other according to the famous equation E = mc²

The SI unit of power, equivalent to one joule per second, corresponding to the rate of consumption of energy (Work done).

If external force is absent then linear momentum of system remains conserved. In collision force of impact due to collision is internal and very large.