Which of the following quantities canNot be a negative number?

Question

A. Temperature, when expressed in kelvins.
B. Pressure, when expressed as gauge pressure.
C. Potential energy, when expressed using the convention that h = 0 at sea level.
D. Internal energy, when expressed relative to a reference state of T = 273.15 K and P = 0.1 MPa.
E. All of the above could be negative numbers.

Answer 1

A. Correct. By definition, 0 K is absolute zero. It is not physically possible to go below this temperature, since it is the temperature at which all energy has been removed from the system.
B. Incorrect. Absolute pressures between 0 and atmospheric pressure correspond to negative gauge pressures.
C. Incorrect. Objects can be located below sea level and these have negative potential energy relative to sea level.
D. Incorrect. Internal energy is considered to be 0 at the reference state, so states with lower internal energy than the reference state (e.g., same pressure but lower temperature) have negative internal energy relative to this reference state, though they have positive internal energy in an absolute sense.
E. Incorrect. Quantities that are expressed on an absolute scale cannot be negative, and one of these is.
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