5. In an open system, for maximum work, the process must be entirely a) irreversible
b) reversible
c) adiabatic
d) none of the mentioned
7. Which of the following is true for a closed system?
a) mass entering = mass leaving
b) mass does not enter or leave the system
c) mass entering can be more or less than the mass leaving
d) none of the mentioned
13. A piston cylinder contains 0.5 kg of air at 500 kPa and 500 K. The air expands in a
process so pressure is linearly decreasing with volume to a final state of 100 kPa and 300
K. Find the work in the process.
a) 56.1 kJ
b) 66.1 kJ
c) 76.1 kJ
d) 86.1 kJ
5- И
Land 279 At this state the

The answer is B. Reversible

B b b b b b b b b b b

An  atom  (ours, not carroll's) consists of a positively charged  nucleus, surrounded by one or more negatively charged particles called  electrons. the positive charges equal the negative charges, so the atom has no overall charge; it is electrically neutral. most of an atom's mass is in its nucleus; the mass of an electron is only 1/1836 the mass of the lightest nucleus, that of hydrogen. although the nucleus is heavy, it is quite small compared with the overall size of an atom. the radius of a typical atom is around 0.1 to 0.25 nanometres (nm), whereas the radius of a nucleus is about 10-6  nm.  *  if an atom were enlarged to the size of the earth, its nucleus would be only 200 feet in diameter and could easily rest inside a small football stadium.read more on -