Physics - Heat & Thermo Question with Solution | TestHub

AB is isobaric: $Q=n{C}_p\Delta T=\frac{5}{2}(4P_1{V}_1-2P_1{V}_1)=5P_1{V}_1\Rightarrow P_1{V}_1=Q/5$

Work on gas in BC: $W_{BC}=\frac{(2P_1+P_1)}{2}{V}_1=\frac{3P_1{V}_1}{2}=\frac{3Q}{10}$ (A correct).

Heat released in BC: $Q_{BC}=\Delta U+W=\frac{9}{2}{P}_1{V}_1+\frac{3}{2}{P}_1{V}_1=\frac{6Q}{5}$, not 2Q/5 (B wrong).

CA is isochoric: $Q_{CA}=\frac{3}{2}(2P_1{V}_1-P_1{V}_1)=\frac{3Q}{10}$ (D correct). Efficiency $=\frac{Q/10}{13Q/10}=\frac{1}{13}$ (C wrong).