Question:
A system does $200 \mathrm{~J}$ of work and at the same time absorbs $150 \mathrm{~J}$ of heat. The magnitude of the change in internal energy is_______J. (Nearest integer)
Solution:
$\mathrm{w}=-200 \mathrm{~J}, \mathrm{q}=+150: \Delta \mathrm{U}=\mathrm{q}+\mathrm{w}$
$\Delta U=150-200=-50 J:$ magnitude $=50 J=|\Delta U|$