In a thermodynamic process, the pressure of a fixed mass of a gas is changed in such a manner that the gas releases 20 J of heat and 8 J of work is done on the gas. If the initial internal energy of the gas was 30 J

Correct answer: C. 18 J Given Δ Q=-20 J, W=-8 J Using Ist law Δ Q=Δ U+Δ W array l Δ Q=-20+8=-12 J Uf=-12+30=18 J array

BITSAT 2014

BITSAT 2014 · Physics · Thermodynamics

In a thermodynamic process, the pressure of a fixed mass of a gas...

In a thermodynamic process, the pressure of a fixed mass of a gas is changed in such a manner that the gas releases

20 \mathrm{ J}

of heat and

8 \mathrm{ J}

of work is done on the gas. If the initial internal energy of the gas was

30 \mathrm{ J}

, then the final internal energy will be

C. $18 \mathrm{ J}$

Given

\Delta \mathrm{Q}=-20 \mathrm{ J}, \mathrm{ W}=-8 \mathrm{ J}

Using Ist law

\Delta \mathrm{Q}=\Delta \mathrm{U}+\Delta \mathrm{W}

\begin{array}{l} \Rightarrow\Delta Q=-20+8=-12 \mathrm{ J}\\ \mathrm{Uf}=-12+30=18 \mathrm{ J} \end{array}