Even a Carnot engine cannot give $100\%$ efficiency because we cannot

$A$ Carnot engine operating between temperatures $600 \,K$ and $300 \,K$ absorbs $800 \,J$ of heat from the source. The mechanical work done per cycle is (in $\,J$)

The efficiency of a Carnot engine operating between reservoirs maintained at temperatures $27^{\circ}C$ and $-123^{\circ}C$ is ...... $\%$

The $p-V$ diagram of a Carnot's engine is shown in the graph below. The engine uses $1$ mole of an ideal gas as the working substance. From the graph,the area enclosed by the $p-V$ diagram is equal to the net work done by the engine. Given that the heat supplied to the gas is $8000 \ J$,calculate the net work done by the engine. (Note: The efficiency of a Carnot engine is $\eta = 1 - \frac{T_2}{T_1} = \frac{W}{Q_1}$) (in $J$)

The efficiency of a Carnot engine operating with reservoir temperatures of $100\,^{\circ}C$ and $-23\,^{\circ}C$ will be

$A$ heat engine receives $200 \, cal$ of heat and rejects $150 \, cal$ of heat. If the temperature of the source is $400 \, K$,what is the temperature of the sink in $K$ (in $, K$)?