Question

What is the work energy principle ?

Answer 1

There is one law which will be valid anywhere and at any situation universally and that law is law of conservation of energy. That means energy can neither be created nor destroyed but it is only converted from one form to the other. By using this law we will solve this problem.

Formula used:
$W = F.x = \Delta KE$

Complete answer:
The units of kinetic energy are joules. The units of work done are also joules. The relation between kinetic energy and work done can be understood by the work-energy theorem.
Work energy theorem states that work done by all the forces combined will result in change in kinetic energy
$W = F.x = \Delta KE$
Where ‘W’ is work done by all the forces and ‘x’ is displacement and ‘F’ is the force and $\Delta KE$ is change in kinetic energy.
Here the work done includes the work done by all kinds of forces i.e by conservative or non conservative or all other external forces.
The basic definition for conservative force is that the work done by the conservative force over the closed loop is zero. Work done by the non conservative force over the loop is not zero.

Hence this is a work energy theorem.

Note:
This work energy theorem is the basis for the conservation of mechanical energy principle. Mechanical energy consists of kinetic energy and potential energy. The term potential energy is used only when there is conservative force. The examples of conservative forces are spring force and gravitational force and electrostatic force. Here only electrostatic force is conservative force but the induced electric field due to magnetism is not conservative force.