The Value of the Momentum of a System Is the Same

Multiple Choice

The value of the momentum of a system is the same at a later time as at an earlier time if there are no

A) collisions between particles within the system.
B) inelastic collisions between particles within the system.
C) changes of momentum of individual particles within the system.
D) internal forces acting between particles within the system.
E) external forces acting on particles of the system.