Does a Carnot engine working under an isothermal state perform any useful work?

An ideal heat engine based on the Carnot cycle operates between temperatures of $227 \, ^\circ C$ and $127 \, ^\circ C$. If it absorbs $6 \times 10^{4} \, cal$ of heat from the high-temperature reservoir,the net work done by the engine is:

$A$ heat engine operates between a cold reservoir at temperature $T_{2} = 400 \, K$ and a hot reservoir at temperature $T_{1}$. It takes $300 \, J$ of heat from the hot reservoir and delivers $240 \, J$ of heat to the cold reservoir in a cycle. The minimum temperature of the hot reservoir has to be $.... K$.

The efficiency of a Carnot cycle is $\frac{1}{6}$. By lowering the temperature of the sink by $65 \ K$,it increases to $\frac{1}{3}$. The initial and final temperatures of the sink are:

$A$ Carnot engine absorbs an amount $Q$ of heat from a reservoir at an absolute temperature $T$ and rejects heat to a sink at a temperature of $T/3$. The amount of heat rejected is

What is a Carnot engine?