Answer:
-30 J
Step-by-step explanation:
The change in internal energy of a system is given by the first law of thermodynamics, which states that the change in internal energy is equal to the heat added to the system minus the work done by the system:
ΔU = Q - W
where ΔU is the change in internal energy, Q is the heat added to the system, and W is the work done by the system.
In this case, 20 J of heat is extracted from the system (i.e., heat is leaving the system), and 10 J of work is done by the system. So we can substitute these values into the formula:
ΔU = -20 J - 10 J
ΔU = -30 J
Therefore, the change in internal energy of the system is -30 J. The negative sign indicates that the internal energy of the system has decreased.