Question

Work-energy theorem is valid in the presence of
A. external forces only
B. internal forces only
C. conservative forces only
D. all type of forces

Answer 1

Hint: Work-energy principle is valid even in the case of any non-conservative force. As we can see that we are making use of the work energy theorem for the work done by the resultant force, this theorem is valid everywhere. Hope these all may help you to solve this question.

Complete answer:
As we all know that all objects in motion are having kinetic energy. Hence there will be a relation between the work done and the kinetic energy. This relationship between the kinetic energy of a body and the work done is known as the “Work-Energy Theorem”. It can be expressed in the form of equation,
$W=\Delta K$

Here, $W$ be the work done in joules $\left( J \right)$ and $\Delta K$ will be the change in kinetic energy of the body. The energy and work done is being scalar quantities, the work done will be given as the resultant sum of individual work done of the bodies. This theorem can be applied in the cases of conservative forces, non-conservative forces, internal forces, external forces and so on. The work energy theorem is valid in any kind of forces.

So, the correct answer is “Option D”.

Note:
Work done is defined as the energy stored or dispersed by a body when a force is acting on the body. That is it is said to be done if the force acting is displacing a particle. If there is no displacement, then the work done by the particle will be zero. Thus, the work will be a cause of force and the net displacement.