Q$1.$ a$)$ When is a system said to be in thermal equilibrium?

b$)$ Mechanical equilibrium is related to pressure. So$,$ when is a system said to be in Mechanical equilibrium?

c$)$ Any change that a system undergoes from one equilibrium state to another is known as a $q,($system$,$ path, state, process, postulate: choose one$).$

d$)$ Among the engineering devices listed below, circle three that operate at steady$-$flow conditions.

$($reciprocating compressors, turbines, power plants, boilers, condensers, compressors$).$