Question

Sir/Mam,can an internal force change both K.E. and momentum of a body?(Neglect all the resisting forces.)

Answer 1

Internal force cannot change the momentum. change in momentum only occur when there is an external force.
Also internal forces can increase the kinetic energy of the body.
In accordance to work-energy theorem, the net work done by the forces acting on a body is equal to the change in the kinetic energy of the body. The work done by internal forces will increase the internal energy of a body. The increase of internal energy of the body results, its constituent atoms or molecules might acquire this energy in several different forms like increase of translational kinetic energy and increase of rotational kinetic energy. Therefore, the work done by the internal forces can increase the kinetic energy of the body