21.In a thermodynamic process, the pressure of a fixed mass of gas is changed in such a manner that the gas molecules give out 30 J of heat and 10 J of work is done on the gas. If the initial internal energy of the gas was 40 J, then the final internal energy will be

22.From what height should a piece of ice fall so that it melts completely ? (Given : one-quarter of the heat produced is absorbed by ice and latent heat is L)

23.An ideal gas with pressure P is compressed isothermally till the mean separation between molecules of the gas is reduced to half of the original value. The final pressure will be

24.A Carnot engine working between 300 K and 600 K has a work output of 800 J per cycle. The amount of heat energy supplied from the source to the engine in each cycle is

25.Two thermometers X and Y are placed inside an enclosure whose walls are maintained at a steady temperature T. When equilibrium is established, X and Y will give the same reading T