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

Options

A. linearmomentum of the system does not change in time
B. kinetic energy of the system does not change in time
C. angular momentum of the system does not chagne in time
D. potential energy of the system does not change in time

Answer

A

Explanation

(a) `Sigma vecF_(ext) = ( d vecP_(system)/(dt)`
Given `Sigma vecF_(ext) = 0 rArr P_(system) = constant`
Due to internal forces acting in the system , the kinetic
and potential energy may change with tiem.
Also zero external force may create a torque if the line
of action of forces are along different direction. Thus
the torque will change the angular momentum of the
system.