State and explain work energy principle. Mention any three examples for it.

Hint: In physics, the concept of work and energy is thoroughly correlated and linked to force. It is because whenever force is applied to any object, there is some work done and also some change in the energy. Work is a physical activity that includes movement in the direction of applied force.

Complete step by step answer:
The increase in kinetic energy of a rigid body is caused by some amount of work done on the body due to the force acting on it. This is known as the work-energy principle. Similarly the decrease in kinetic energy is brought about by the negative work done by force acting on the body.
The three examples are
1) A car moving in with constant velocity is accelerated. Hence there is an increase in velocity. So kinetic energy is increased by the positive work done by the engine.
2) A ball dropped from a height H. Work done by gravity increases the velocity of the ball and thus kinetic energy increases.
3) Brakes are applied in a motor bike and it comes to rest after a few seconds. Here work done by the break is negative. So with decrease in velocity, kinetic energy decreases.

Note: Work is said to be accomplished only if there is some displacement of the object. In case of no displacement, but the force is applied, then the work done is zero. However, energy does not depend on whether some displacement is or not. For example, a man pushing a wall is applying force to move to a certain distance. The wall does not move, and hence the work done comes out to be zero.