If the door of a refrigerator is kept open in a closed room,will the room become cooler or warmer?

An ideal heat engine has an efficiency $\eta$. The coefficient of performance of the engine when driven backward will be

The coefficient of performance of a Carnot refrigerator working between temperatures $30 \, ^\circ\text{C}$ and $0 \, ^\circ\text{C}$ is:

$A$ Carnot heat engine has an efficiency of $10 \%$. If the same engine is worked backward to obtain a refrigerator,then the coefficient of performance of the refrigerator is

In a cold storage,ice melts at the rate of $2 \ kg$ per hour when the external temperature is $20^{\circ} C$. The minimum power output of the motor used to drive the refrigerator which just prevents the ice from melting is (latent heat of fusion of ice $= 80 \ cal \ g^{-1}$) (in $W$)

The specific heat capacity of a metal at low temperature $T$ is given as $C_p = 32 \left( \frac{T}{400} \right)^3 \text{ kJ K}^{-1} \text{ kg}^{-1}$. $A$ $100 \text{ g}$ vessel of this metal is to be cooled from $20 \text{ K}$ to $4 \text{ K}$ by a special refrigerator operating at room temperature $27^\circ \text{C}$. The amount of work required to cool the vessel is