Question

In a thermodynamic process, $50J$ of heat is going out of the system and $10J$ of work is done on the system. If the initial internal energy of the system was $60J$, then the final internal energy of the system will be

• A. $Zero$
• B. $20J$
• C. $-20J$
• D. $120J$

Answer 1

The correct option is B $20J$

$dQ=-50J$ (negative because heat is going out of the system)
$W=-10J$ (work done on the system)
$U_i=60J$
$dQ=dU+W$
$-50=(U_f-60)+(-10)$
$U_f=20J$