Answer :
Final answer:
The change in thermal energy of the system is 35 J.
Explanation:
The change in internal energy of a system can be determined by using the first law of thermodynamics, which states that the change in the internal energy of a system (ΔU) is equal to the heat (ΔQ) added to the system minus the work (ΔW) done by the system:
ΔU = ΔQ - ΔW
From the student's question, we have the work done on the system as 15 J and the heat transferred out of the system as 20 J. However, when work is done on the system, it should be considered positive, and heat transferred out should be negative. Thus:
ΔU = (+15 J) - (-20 J)
ΔU = 15 J + 20 J
ΔU = 35 J
The change in thermal energy of the system is 35 J.
