The Question as Posted (Incorrect / Ambiguous)
- The Navier-Stokes equations mathematically describe fluids by combining:
a. Conservation of mass
b. Conservation of momentum
c. Conservation of energy
d. All of the above
Comment
The wording of this question is scientifically inaccurate and misleading.
Strictly speaking, the Navier–Stokes equations themselves represent the conservation of momentum, derived directly from Newton’s second law applied to a fluid element.
They do not result from combining:
conservation of mass,
conservation of momentum,
and conservation of energy.
Instead, a complete mathematical description of fluid flow requires a system of governing equations, namely:
the continuity equation (conservation of mass),
the Navier–Stokes equations (conservation of momentum),
and the energy equation (conservation of energy, when thermal effects are considered).
Therefore, while option (d) “All of the above” may appear correct in a very general or introductory context, the question as stated confuses the Navier–Stokes equations with the full set of governing equations of fluid motion.
✅ Suggested correct rephrasing:
The equations governing fluid motion are based on:
a. Conservation of mass
b. Conservation of momentum
c. Conservation of energy
d. All of the above
