How Do You Calculate Kinetic Energy in First Law Thermodynamics Problems?

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When asked to calculate the change in kinetic energy of a system, do you calculate the kinetic of the entire system as if it was moving? Or do you calculate the kinetic energies of the various subsystems within the systems and then add it up so that you have the total kinetic energy?
 
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Usually kinetic energy is defined through the motion of the center of mass. Motion of subsystems with respect to the center is then classified to angular momentum, temperature, etc., which are not included in K.E.
 
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