What is the essential reason that all perpetual motion machines ...

[ashley]

What is the essential reason that all perpetual motion machines fail?
 a. Perpetual motion machines must create energy in order to do useful work, and energy cannot be created.
  b. Perpetual motion machines must at least preserve all the energy in a system, and some is always lost.
  c. Perpetual motion machines run on gasoline, and gasoline is not a renewable resource.
  d. A perpetual motion machine necessarily removes heat from a single-temperature environment.
  e. Perpetual motion machines have to contend with friction, which destroys energy.

Question 2

A refrigerator uses mechanical work to transfer heat from a colder region to a hotter one, as shown in this schematic. Why is it not possible to remove heat from the cold region and transfer it to the hot region without the input of work by an external source?
 a. It would violate the first law of thermodynamics.
  b. It would violate the second law of thermodynamics.
  c. Both a. and b.
  d. It would be possible only if the machine did not lose some energy as heat because of friction.

[Li Jun]

Answer to Question 1

b

Answer to Question 2

b