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

The correct option is A Increase by $30$ $kJ$

$q=50$ kJ (as heat is absorbed, so it is positive)

$w=-20$ kJ (as work is done by the system, so it is negative)

$\therefore \Delta U=q+w=50-20=30kJ$

Therefore, internal energy change increases by $30$ $kJ.$

Hence, the correct answer is option $\text{A}$.