What is the relationship between the total energy(E),kinetic energy(K),potential energy (P) of a system?
(A) $K = P + E$
(B) $E = P + K$
(C) $P = K + E$
(D) $E = PK$

Hint: Total mechanical energy of the system is equal to the sum of kinetic energy of the system and the potential energy of the system.

Complete answer:
An object possesses energy when it has a capability to do work. Activities like cooking food, dancing on music, singing a song requires energy. Life is impossible without the energy. Sun is the biggest natural source of free energy. An object that possesses energy can exert a force on another object and energy is transferred from the former to the latter. The second object moves as it receives energy and therefore does some work. This implies that any object that possesses energy can do work.
When an object is in motion, it possesses energy that is called kinetic energy. Activities like riding horses, driving cars, rolling stones, flying planes are examples of kinetic energy. The kinetic energy of an object increases with its speed.
The potential energy possessed by the object is the energy present in it by virtue of its position or configuration that means potential energy is stored energy in the object when work is done on the object but there is no change in the velocity or speed of the object.
Total energy of a body is the sum of kinetic energy and the potential energy of the system.
 Thus, total mechanical energy: $E = P + K$

Note:
Law of conservation of energy:
Total energy of the system remains unchanged when energy is transformed. Energy can neither be created nor destroyed but only converted from one form to another. The total energy before and after the transformation remains the same. This is called the law of conservation of energy.