Bukhovtsev-et-al-Problems-in-Elementary-Physics

74 PROBLEMS
pressure Po = 760 mm Hg. The temperature in the lake t = +4° C.
Disregard the tension of the rubber.
328. Two hollow glass balls are connected by a tube with a
drop of mercury in the middle. Can the temperature of the ambient
air be appraised from the position of the drop?
329. A cylinder closed at both ends is separated into two
equal (42 em each) parts by a piston impermeable to heat. Both
the parts contain the same masses of gas at a temperature of
27°C and a pressure ofl atm.
How much should the gas be heated in one part of the cylinder
to shift the piston by 2 cm? Find the pressure p of the gas
after shifting of the piston.
330. Dry atmospheric air consists of nitrogen (78.09 per cent
by volume), oxygen (20.95 per cent), argon (0.93 per cent) and
carbon dioxide (0.03 per cent). Disregarding the negligible admixtures
of other gases (helium, neon, krypton, xenon), determine
the composition of the air (in per cent) by weight.
331. Find the mean (effective) molecular weight of dry atmospheric
air if the composition of the air in per cent is known
(see Problem 330).
332. The density of the vapour of a compound of carbon and
hydrogen is 3 g/lit at 43°C and 820 mm Hg. What is the molecular
formula of this compound?
333. When will the change in the pressure of a gas be greater-if
it is compressed to a certain extent in a heat-impermeable
envelope or upon isothermal compression?
334. A gas that occupies a volume of VI = 1 lit at a pressure
of PI = I atm expands isothermally to a volume of VI = 2 lit.
Then, the pressure of the gas iii halved at the same volume.
Next the gas expands at a constant pressure to V4 = 4 litres.
Draw a diagram of p versus V and use it to determine the
process in which the gas performs the greatest work. How does
the temperature change?
335. A cyclic process 1-2-3-1 depicted on a V-t diagram
(Fig. 130) is performed with a certain amount of an ideal gas, .
Show the same process on a p-V diagram and indicate the
stages when the gas received and when it rejected heat.
336. A gas heated geyser consumes V o = 1.8 m" of methane
(CH c ) an hour. Find the temperature tt of the water heated
by the geyser if the water flows out at a rate of v = 50 crn/s.
The diameter of the stream D = I ern, the initial temperature
of the water and the gas t 1 = 11 0 C and the calorific value of