# Aerodynamics Questions and Answers – Continuity Equation

This set of Aerodynamics Multiple Choice Questions & Answers (MCQs) focuses on “Continuity Equation”.

**1. For an incompressible flow, the mass continuity equation changes to ________**

a) energy equation

b) momentum equation

**c) volume continuity equation**

d) remains same

**Explanation:** ∇.u=0 – The flow velocity is u in this equation, and the divergence of flow velocity is zero. The density of the flow remains constant since it is incompressible, and hence the volume cannot be modified.

**2. Which of the flowing is an example of incompressible flow?**

a) gas

b) sponge

**c) water**

d) gel

**Explanation:** The term “incompressible flow” refers to a flow with a constant density. Because the water molecules are so close together, the intermolecular distance is incredibly short. As a result, the water is impermeable.

**3. The differential form of continuity equation is __________**

a) ∇.u=constant

b) Dv/Dt=0

**c) ρ/t + ∇.(ρV)=0**

d) ρ=0

**Explanation:** ρ-density V-velocity vector t-time

The inflow and outflow are represented by the divergence, whereas the accumulation of mass inside a body is represented by the time derivative. It states that the amount of mass that enters the body is equal to the amount of mass that leaves it.

**4. The equation which results in the change in pressure with change in the vertical height is called as ______**____

a) energy equation

b) momentum equation

c) continuity equation

**d) hydrostatic equation**

**Explanation**: dp = -g dp = -g dp = -g dp = The hydrostatic equation is represented by dy, where p is the pressure acting on a body, g is the acceleration due to gravity, and dy is the change in vertical height. The element’s net force acts exclusively in one direction: vertically. The front and back faces have equal and opposite pressure forces, which cancel each other out.

**5. When Reynold’s number limits to infinity, inviscid flow is approached.**

**a) True**

b) False

**Explanation:** Friction, thermal conduction, and diffusion impact inviscid flows are limited to a very narrow band next to the body surface called the boundary layer, and the flow outside of this small region is virtually inviscid.

**6. Mass can neither be created nor be destroyed is the principle of_______**

a) Energy equation

b) Momentum equation

**c) Continuity equation**

d) Bernoulli’s principle

**Explanation:** The mass conservation principle underpins the continuity equation. Unless and until mass is added or removed from the system, the amount of mass in any system remains constant, according to this law. This suggests that the amount of matter in the universe remains constant.

**7. If the system is in steady state, it is in an equilibrium state.**

a) True

**b) False**

**Explanation: T**he fact that the system is in a steady state does not imply that it is in an equilibrium state. The system is in a steady state if it is in an equilibrium state. When all of the thermodynamic properties of a system are fixed, it is said to be in equilibrium. If energy is dissipated inside a system, it is considered to be in a steady state.

**8. Continuity equation is related to _______**

**a) Mass conservation**

b) Energy conservation

c) Momentum conservation

d) Velocity change

**Explanation:** Continuity equation is related to mass conservation. It states that the total mass entering a body is equal to the total mass leaving a body.

Mass entering the body = mass leaving the body.

**9. The quantity specifying the flow or motion is termed as _________**

a) Density

**b) Flux**

c) Field

d) Electrostatic force

**Explanation:** Flux density is another name for flux. It refers to how much quantity (q) is flowing per unit volume (v). The quantity should be able to move or flow in some way.

**10. In electromagnetic theory, continuity equation relates _______**

a) Volume conservation

b) Mass conservation

**c) Charge conservation**

d) Energy conservation

**Explanation:** Charge conservation is a result of Maxwell’s equation, which asserts that the divergence of current density equals the negative rate of change of charge density in electromagnetic theory.

∇.J=- ρ/t

Where J-current density and ρ-charge density.

The continuity equation (Eq. 4.1) states that mass in the pipeline is conserved: mass in minus mass out = change in mass. “Mass flow in minus mass flow out” of a slice of the pipeline cross-section is the first term in the equation, ( v A ) / x. The continuity principle, often known as the continuity equation, is a fluid mechanics principle. Simply put, what flows into a specified volume during a defined time period, minus what flows out of that volume over that time period, must accumulate in that volume. The principle is a result of the law of mass conservation.