JEE Advanced 2009 Physics 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

(A)linear momentum of the system does not change in timeCorrect
(B)kinetic energy of the system does not change in time
(C)angular momentum of the system does not change in time
(D)potential energy of the system does not change in time

Answer: (A)

Solution

Zero net external force means : linear momentum is conserved (A). Internal forces can still do work, so kinetic and potential energies may change (B, D not

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Question ID VK-037719