Problem description:
Specifically, when inelastic collision occurs, energy is lost, but momentum is still conserved. . .
Analysis:
According to Newton's third law, the internal forces of interaction are always equal in size, opposite in direction and equal in action time, so their impulse problems are equal in size and opposite in direction, and the total impulse to the system is zero, so the total momentum of the system remains unchanged, that is, momentum conservation.
But internal forces can change the energy of the system by doing work. If the total work done by this pair of acting force and reaction force is zero, the mechanical energy of the system is conserved, which is called elastic collision; If the total work done by this pair of action and reaction is negative, the mechanical energy decreases, that is, the mechanical energy loss, which is called inelastic collision.