Self-Test 4B.1A

[Ambar Zamuria 1E]

I am confused about why the answer is -740. kJ instead of +740. kJ. Can someone please explain to me why it is negative and not positive?

[Giuliana_Ming_2D]

Hi! The work is negative because when the engine doing that work it is losing energy, so that 520 kJ of work is negative. Then, the 220 kJ of energy is lost as heat, so it's also negative. -520 kJ-220 kJ = -740kJ. Hope this helps!

[Stella Gray 2E]

The answer is negative because work requires energy so the system would lose energy when doing work and also lose energy as heat as stated in the question. So, we can model the change in internal energy as -520-220 = -740 kJ.