How much energy is produced in the burning of $1\, kg$ of coal?

The temperature of $5$ moles of a gas at constant volume is changed from $100^{\circ} C$ to $120^{\circ} C$. The change in internal energy is $80 \,J$. The total heat capacity of the gas at constant volume in $J/K$ is:

$A$ small electric heater is used to heat $200 \,g$ of water. The time required to bring all this water from $40^{\circ} C$ to $100^{\circ} C$ is $200 \,s$. If the specific heat of the water is $4200 \,J \,kg^{-1} \,K^{-1}$, then the power supplied by the heater is: (in $\,W$)

$A$ substance is cooled at a constant power. Its temperature vs time graph is shown. The value of $S_{solid} : S_{liquid} : S_{gas}$ is:

Which of the following is the unit of specific heat?

In engines,water is used as a coolant because ......