Two aluminum blocks are in thermal contact. 

(a) Are the blocks necessarily in physical contact? Explain. 

(b) If they have the same temperature, do they necessarily have the same internal energy? Explain. 

(c) If their internal energies are not equal, is there necessarily a net energy transfer between the two blocks? Explain. 

(d) One block has mass 1.00 kg and temperature 40.0°C. The other has mass 3.00 kg and temperature 20.0°C. Find the final equilibrium temperature and the changes in internal energy of each block.