$10 \, g$ of ice at $0^{\circ} C$ is kept in a calorimeter of water equivalent $10 \, g$. How much heat (in $cal$) should be supplied to the apparatus to evaporate the water thus formed? (Neglect loss of heat)

$10\, g$ of a lead bullet travelling at $300\, m/s$ strikes against a block of wood and comes to rest. Assuming $50\%$ of the heat produced is absorbed by the bullet,the increase in its temperature is ........ $^\circ C$. (Specific heat of lead $= 150\, J/kg\cdot K$)

The top of a lake gets frozen at a place where the surrounding air is at a temperature of $-20\,^oC$. Then

$A$ hammer of mass $1 \, kg$ having a speed of $50 \, m/s$ hits an iron nail of mass $200 \, g$. If the specific heat of iron is $0.105 \, cal/g^{\circ}C$ and half of the kinetic energy is converted into heat,the rise in temperature of the nail is ........ $^{\circ}C$.

$A$ water cooler of storage capacity $120$ litres can cool water at a constant rate of $P$ watts. In a closed circulation system (as shown schematically in the figure),the water from the cooler is used to cool an external device that generates constantly $3 \text{ kW}$ of heat (thermal load). The temperature of water fed into the device cannot exceed $30^{\circ}\text{C}$ and the entire stored $120$ litres of water is initially cooled to $10^{\circ}\text{C}$. The entire system is thermally insulated. The minimum value of $P$ (in watts) for which the device can be operated for $3$ hours is (Specific heat of water is $4.2 \text{ kJ kg}^{-1} \text{K}^{-1}$ and the density of water is $1000 \text{ kg m}^{-3}$)

$A$ closed bottle containing water at $30^{\circ} C$ is opened on the surface of the moon. Then,