Clarification on Quiz 1 Prep - Question 2

[Cecile Riviere-Cazaux 2A]

For the quiz 1 preparation, my TA told us that the answer was 5 kJ. But, if the question is asking for delta U, and it is an isolated system, shouldn't the answer be 0 kJ?

For reference, the question is: if an isolated system contained +5 kJ of energy, after 100 years delta U = ?

Thanks!

[vsyacoubian2A]

The answer should be delta U= 0. Conceptually, if I put 5 kj of energy in a bank, and I didn't touch it for 100 years, I will still have 5 kj of energy in the bank. Since there is no change in energy, then delta U=0

[Alondra Cervantes 1F]

Make sure to understand that an isolated system means that it can't exchange anything with outside boundaries. Which is why the change in U is 0, since nothing every changed with the system.