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# If the resultant of all external forces acting on a system of particles is zero, then from an inertial frame, one can surely say that

a) linear momentum of the system does not change in time.

b) Kinetic energy of system does not change in time.

c) Angular momentum of system does not change in time.

d) potential energy of system does not change in time .

It is inertial frame, it means that the frame of reference does not have an acceleration, and so does not have a psudo force
$\sum F = 0,=>\large\frac{dp}{dt}=0$
$p$ is constant
kinetic energy and potential energy does not remain constant
Hence a is the correct answer.
edited Mar 14, 2014 by meena.p