Physics - Heat & Thermo Question with Solution | TestHub

Key Idea Heat given to a system ( $\Delta Q$ ) is equal to the sum of increase in the internal energy $(\Delta \mathrm{u})$ and the work done $(\Delta W)$ by the system against the surrounding and $1\mathrm{cal}=4.2\mathrm{J}$. According to first law of thermodynamics $$\begin{array}{rl}\Delta \mathrm{U}& =\mathrm{Q}-\mathrm{W}\\ & =2\times 4.2\times 1000-500\\ & =8400-500\\ & =7900\mathrm{J}\end{array}$$