Question

Can work energy theorem be applied only on a single object and not on a system ?

Answer 1

Dear student,
Work energy theorem suggests:
work done on an object = change in the kinetic energy of the object.
So, to determine work done on an object (particle or rigid body) we just need to know the change in its kinetic energy. Thus, this theorem is perfectly valid in either cases.
Furthermore, large bodies are treated as point objects in-order to carry out calculations conveniently. And the good thing is, it works.
Regards