Question

$A$ system absorbs $50 \,kj$ heat and does $20\, kj$ of work. What is the net change in the internal energy of the system?

• A. Increase by $30\, kj$
• B. Decrease by $30\, kj$
• C. Increase by $70 \,kj$
• D. Decrease by $70 \,kj$

Answer 1

Answer: (A)

Increase by $30\, kj$

Answer 2

$\Delta U =q + (-w) = 50 + (-20) = 30\, kj$