Lesson: The First Law of Thermodynamics

Some liquid in a sealed container receives a net heating, , of 125 J from its surroundings, causing it to expand slightly, as shown in the diagram. The liquid expands more than the container does, and the greater expansion of the liquid exerts a pressure on the container, which deforms it. The elastic potential energy increase due to the container’s deformation is 15 J. What is the change in the internal energy of the liquid?

Which of the following formulas correctly represents the change in internal energy of a system, where is the net heating of the system and is the net work done by the system?

An electric drill has an average useful output power of 55 W during 0.45 s of operation. The power output of the drill is transferred to a brick that has a specific heat capacity of 850 J/kg⋅K and a mass of 1.5 kg. The drill and the brick are initially at the same temperature. Because of friction, the brick increases in temperature by 0.012 K while in contact with the drill bit. What is the net useful work done on the brick by the drill if the drill bit is heated by 0.25 J? Answer to three significant figures.