A lead bullet at $27\,^oC$ just melts when stopped by an obstacle. Assuming that $25\%$ of heat is absorbed by the obstacle, then the velocity of the bullet at the time of striking is ........ $m/s$ ($M.P.$ of lead $= 327\,^oC,$ specific heat of lead $= 0.03\,cal/g\,^oC,$ latent heat of fusion of lead $= 6\,cal/g$ and $J = 4.2\,joule/cal$ )
$410$
$1230$
$307.5$
None of the above
If there are no heat losses, the heat released by the condensation of $x$ gm of steam at $100^o C$ into water at $100^o C$ can be used to convert $y$ gm of ice at $0^o C$ into water at $100^o C$. Then the ratio $y : x$ is nearly
Steam at $100\,^oC$ is passed into $22\,g$ of water at $20\,^oC$ The mass of water that will be present when the water acquires a temperature of $90\,^oC$ (Latent heat of steam is $540\,cal/g$) is ......... $\mathrm{g}$
Suppose there is a hole in a copper plate. On heating the plate, diameter of hole, would
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
A solid cube having certain fixed melting and boiling points takes heat from some source. The variation of temperature $\theta$ of the cube with the heat supplied $Q$ is shown in the adjoining graph. The portion $BC$ of the graph represents the conversion of