Question

On which of these following options is the continuity equation based?

(a) Work energy theorem

(b) Law of conservation of energy

(c) Conservation of mass

(d) Conservation of momentum

This question was posed to me during an internship interview.

The origin of the question is Fluids Mechanical Properties topic in division Mechanical Properties of Fluids of Physics – Class 11

Answer 1

Right choice is (c) Conservation of mass

The explanation: The continuity equation is based on the conservation of mass. We consider that fluid is incompressible (constant density) and say that mass of fluid passing through 2 different regions at the same time is the same.

∴ density X Vol1 = density X Vol2.

∴ Vol1 = Vol2.

∴ A1v1Δt = A2v2Δt

∴ A1v1 = A2v2.