Liquid oxygen at $50\  K$ is heated to $300\  K$ at constant pressure of $1\  atm$. The rate of heating is constant. Which of the following graphs represents the variation of temperature with time ?

A lead bullet at $27\ ^oC$ just melts when stooped by an obstacle. Assuming that $25\%$ of heat is absorbed by the obstacle, then the velocity of the bullet at the time of striking  ....... $m/s$  ( $M.P.$ of lead $= 327\,^oC$ , specific heat of lead $= 0.03\,cal/g\,^oC$ , latent heat of fusion of lead $= 6\,cal/g$ and $J = 4.2\,joule/cal$ )

Solids expand on heating because ................

$200\, g$ of a solid ball at $20\,^oC$ is dropped in an equal amount of water at $80\,^oC$. The resulting temperature is $60\,^oC$. This means that specific heat of solid is

Explain why :

$(a)$ a body with large reflectivity is a poor emitter

$(b)$ a brass tumbler feels much colder than a wooden tray on a chilly day

$(c)$ an optical pyrometer (for measuring high temperatures) calibrated for an ideal black body radiation gives too low a value for the temperature of a red hot iron piece in the open, but gives a correct value for the temperature when the same piece is in the furnace

$(d)$ the earth without its atmosphere would be inhospitably cold

$(e)$ heating systems based on circulation of steam are more efficient in warming a building than those based on circulation of hot water

On a new scale of temperature (which is linear) and called the $W$ scale, the freezing and boiling points of water are $39\,^oW$ and $239\,^oW$ respectively. What will be the temperature on the new scale, corresponding to a temperature of $39\,^oC$ on the Celsius scale ? ............. $^\circ \mathrm{W}$