2. (a) The piston is frictionless and leak proof and the expansion may be assume

Question

2. (a) The piston is frictionless and leak proof and the expansion may be assumed reversible. Calculate the gas pressure in the cylinder of the machine shown below when: (i) the atmospheric pressure is 14.7 Ibf / in2 absolute (psia); (ii) the surroundings' absolute pressure is zero. (b) Calculate the reversible work done by system A from the changes in the system's properties (the pressure and volume change). Compare with the result in problem 1 (a). (c) Is it possible to calculate the work from information concerning the system properties when the external pressure is absolute zero? Why or why not? (d) Suggest a design change in this machine that would decrease the work of atmospheric displacement without changing the useful (mass-raising) work. Would this change affect the cylinder pressure?

Explanation / Answer

a)i) P=14.7+mg/A

ii)P=mg/A

b)for a piston cylinder arrangement pressure is going to be same for reversible process

therefore W = P(Vf-Vi)    V-volume(final-f ,initial-i)

Q = U + W

c)the work done by gas as it expands goes in increasing the PE of the mass m thus if the hieght increase/decrease of piston is known W =mgh+ Patm*A

d)reduce area of piston

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