Gino Says That the Analog of Gauss's Law for the Flow

question 17

Multiple Choice

Gino says that the analog of Gauss's law for the flow of an incompressible fluid of density ρ at constant velocity is for an imaginary surface within the fluid. Lorenzo says that it is true only if the area where the fluid enters the surface and the area where it leaves the surface are both perpendicular to the velocity of the fluid. Which one, if either, is correct?

• A) Gino, because as much fluid leaves as enters.
• B) Lorenzo, because is not equal to zero if the fluid enters or exits at angles other than 90°.
• C) Lorenzo, because this is true only when the fluid executes rotational motion.
• D) Gino, because it is true only when the fluid is enclosed on all sides, not when it is flowing.
• E) Lorenzo, because it is true only when the fluid is enclosed on all sides, not when it is flowing.