Final answer:
True, a pressure regulator valve is used to control the pressure of the liquid going to the nozzle on a power rig. The absolute pressure in the hose is greater than the nozzle pressure, with the pressure at the nozzle exit being atmospheric.
Step-by-step explanation:
The statement that the device installed on a power rig to control the pressure of the liquid going to the nozzle is the pressure regulator valve is true. Pressure regulators are used to maintain a constant output pressure regardless of variations in the input pressure and flow rates. In the context of fluid mechanics, according to Bernoulli's principle, the absolute pressure in the hose will indeed be greater than in the nozzle if the velocity of the fluid (v) is greater in the nozzle. Since the nozzle discharges into the atmosphere, the pressure at the nozzle exit (P₂) will be atmospheric pressure, assuming no other changes in conditions.