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Question:

If the resultant of all the external forces acting on a system of particles is zero, then from an inertial frame, one can surely say that: linear momentum of the system does not change in time; angular momentum of the system does not change in time; potential energy of the system does not change in time; kinetic energy of the system does not change in time.

kinetic energy of the system does not change in time

angular momentum of the system does not change in time

potential energy of the system does not change in time

linear momentum of the system does not change in time

Solution:

We know that Newton's second law is valid in an inertial frame and the law states that, Linear momentum remains constant if net external force on the system of particles is zero. Fresultant=dP/dt Hence, since Fresultant=0, we can say that momentum of system will not change with time.