$A$ lead bullet at $27^{\circ}C$ just melts when stopped by an obstacle. Assuming that $25\%$ of the heat produced is absorbed by the obstacle,find the velocity of the bullet at the time of striking in $m/s$. (Melting point of lead $= 327^{\circ}C$,specific heat of lead $= 0.03 \, cal/g^{\circ}C$,latent heat of fusion of lead $= 6 \, cal/g$,and $J = 4.2 \, J/cal$)

Fill in the blanks:
$1.$ The temperature of freezing point ...... and temperature of boiling point ...... are taken in a Fahrenheit thermometer.
$2.$ The zeroth law of thermodynamics defines ...... and the first law of thermodynamics defines ......
$3.$ At ...... temperature,water and water vapour have equal density.
$4.$ The ...... has the maximum value of specific heat.

What are freezing and freezing point?

The amount of heat required to change $1 \, g$ of ice at $0^\circ C$ into water at $100^\circ C$ is ............ $cal$.

Explain why:
$(a)$ Two bodies at different temperatures $T_1$ and $T_2$,if brought in thermal contact,do not necessarily settle to the mean temperature $(T_1 + T_2) / 2$.
$(b)$ The coolant in a chemical or a nuclear plant (i.e.,the liquid used to prevent the different parts of a plant from getting too hot) should have high specific heat.
$(c)$ Air pressure in a car tyre increases during driving.
$(d)$ The climate of a harbour town is more temperate than that of a town in a desert at the same latitude.

Thermal expansion due to an increase in temperature...