Figure shown a vertical cylindrical vessel separated in two parts by a frictionless pistion free to move along the length of the vessel. The length of the cylinder is and the pistion divides the cylinder in the ratio of
.Each of the two parts of the vessel contains 0.1 mole of an ideal gas. The temperature of the gas is
in each part. Calculate the mass of the piton.

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Let and
be the lengths of the upper part and the lower part of the cylinder respectively. clearly,
and
. Let the perssures in the upper and lower parts be
and
respectively. Let the area of coss-section of the cylinder be
. The temperature in both parts is
.
Consider the equilibrium of the piston. The forces acting on the pistion are
(a) its weight mg
(b) A downward, by the upper part of the gas and (c)
upward, by the lower part of the gas.
Thus,
Using for the upper and the lower parts
Putting and
from (ii) and (iii) into (i),
Thus,
.