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What is relative velocity? in which condition is relative velocity known by adding the velocity of the first body and that of the second body

If 2 moles of co_2 at 2l and 500k are expanded reversibly to 20l, more work can be obtained from an adiabatic process than from an isothermal process. is the above statement true or false?

Consider a system with two masses that are moving away from each other. why will the kinetic energy differ if the frame of reference is a stationary observer or one of the masses?