Two aluminum bars of the same temperature have different masses. Which bar has the greatest internal energy?

The internal energy of a body is the sum of the kinetic energies of the energies of the chaotic motion of all particles relative to the center of mass of the body, and the potential energies of their interaction with each other. Kinetic energy is determined by the speed of movement of particles, and therefore by the temperature of the body. The potential energy is determined by the distance between the particles, and hence by the volume of the body. Since both bars are made of aluminum, a bar with a larger mass will have a larger volume, which means more internal energy.

Answer: a bar with a large mass has a large internal energy.