If there is no external force acting on a non-rigid body which of the following quantities must remain constant?

Let L be the Angular momentum.


Then


External torque



When external force is zero, , that means



This condition becomes true when, L remains constant because differentiation of a constant becomes zero.


Hence, angular momentum, L remains constant if external torque is zero


Similarly,


Linear momentum p-



External force,



Hence


P remains constant if external force is zero


Hence, in the absence of external forces, angular momentum and linear momentum of system is conserved.


A change in Kinetic Energy can be seen as in case of inelastic collision.


Similarly, moment of inertia may also change in this case.

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