After a system is added 40-J heat, the system does 30-J work. How do you find the change of the system’s internal energy?

1 Answer
Mar 20, 2018

10J

Explanation:

1st Law of Thermodynamics:
DeltaU=Q-W
DeltaU= change in internal energy.
Q= Heat energy supplied .
W= work done by the system.

DeltaU=40J-30J=10J

Some physicist and engineers use different signs for W.

I believe this is the engineer's definition:
DeltaU=Q+W here, W is the work done on the system.
The system does work of 30J hence the work done on the system is -30J.