Question

A system is given $400\text{cal}$ of heat and $1000\text{J}$ of work done by the system, then the change in internal energy of the system will be

• A. $-860\text{J}$
• B. $680\text{erg}$
• C. $680\text{J}$
• D. $860\text{J}$

Answer 1

The correct option is C $680\text{J}$

$1\text{cal}=4.184\text{J}$, thus $400\text{cal}=1673.6\text{J}$
The change in internal energy is $\Delta U=\Delta Q-\Delta W$
or $\Delta U=1673.6-1000=673.6\approx 680\text{J}$