In this system, the correct description of the energy transfer is:
Thermal energy from the coffee is transferred to the mug.
As the hot coffee cools, its thermal energy decreases, leading to a decrease in the average kinetic energy of the particles in the coffee. At the same time, the mug absorbs thermal energy from the coffee, causing the mug's temperature to increase, which means the average kinetic energy of the particles in the mug increases.
Therefore, the other options are not accurate in the context you provided:
- The average kinetic energy of the particles in the mug increases, not decreases.
- The average kinetic energy of the particles in the coffee decreases, not increases.
Thus, the main energy transfer in your system is indeed from the coffee to the mug.