Fluid Mechanics Objective Questions (MCQ) part-02

Fluid Mechanics Objective Questions (MCQ)

6. Which of the following is NOT a kind of force considered in the Navier-Stokes equation?

a) Gravity force

b) Pressure force

c) Surface tension force

d) Viscous force

Answer: c

Explanation: gravity, pressure force, and viscous forces together they constitute the derivation of the Navier-Stokes equation. Although the surface tension force acts on a moving fluid, it is considered negligible for the Navier-Stokes equation.

7. Fluid is said to be ideal?

a) non-viscous and incompressible

b) Viscous and compressible

c) Viscous and incompressible

d) incompressible

Answer: a

Explanation: Ideal fluids are fluids that have zero viscosity. This result in a flow called invisible flow. The invisible flow is non-viscous and incompressible since there is no shear force due to zero viscosity.

8. If a flow has the same parameters at any given point, then it is said

to be_________

a) Uniform flow

b) Quasi-static flow

c) Laminar flow

d) Static flow

Answer: d

Explanation: A flow that takes place at a constant speed without the change in cross section is called uniform flow. Its parameters remain constant at any given point.

9. Bernoulli's equation in fluid dynamics is valid for ____

a) Compressible flows

b) Temporary flows

c) Continuous flows

d) Viscous flows

Answer: c

Explanation: To answer this equation, we need to understand the assumptions utilized in Bernoulli's equation. Bernoulli's theorem is only valid for ideal, constant, in-compressible, continuous, invisible, and ir-rotational flows. So, out of the options, only continuous flows fit into the assumptions.

10. Water flows through a pipe at a speed of 2 m/s. The pressure gauge reading is 2 bars. The reference height is given in 2 m. Find the piezometric head.

  (Assume all Bernoulli assumptions, Density of water = 1000 kg/m3, g = 9.8 m/s2).

a) 22.4m

b) 22.6m

c) 20.4m

d) 20.6m

Answer: a

Explanation: 

The piezometric head is the addition of the pressure head

and the reference head. 

The pressure head is given by 

           P / ρg = 20.4 m. 

The reference height is 2 m, 

which makes a total of 22.4 m. 

The speed given is additional information.

11. A student wants to find the speed of air flowing through a pipe. He has a pressure gauge that shows only the dynamic pressure. The manometer reads 0.018 mm Hg.

 Assume the density of air is 1.225 kg/m3, 

find the velocity V of the air (ρg = 20.4 m, Hg = 13600 kg/m3).

a) 4 m/s

b) 2 m/s

c) 20 m/s

d) 40 m/s

Answer: b

Explanation: (0.018 mm Hg * 13.6 * 9.8) = 2.4 bar. 

The dynamic pressure is given by ρg = 20.4 m.V 2 /2. 

Equating 2.4 bar with dynamic pressure gives V = 2 m/s.

12. If the compressibility force and the surface tension force are neglected from Newton's second law of motion, which of the following equations results?

a) Navier-Stokes equation

b) Euler's equation

c) Bernoulli's equation

d) Reynolds equation

Answer: d

Explanation: Newton's second law of motion is made up of 6 forces, namely gravity, viscosity, pressure, turbulence, surface tension and compressibility forces. The Reynolds equation is made up of 4 forces. The surface tension force and the compressibility forces are neglected to find the Reynolds equation.

13. What does a Pitot tube measure? On what principle does a Pitot tube work?

a) Pressure, Bernoulli's principle

b) Velocity, Bernoulli's principle

c) Pressure, Euler equation

d) Velocity, Euler's equation

Answer: a

Explanation: Although a Pitot tube can be used primarily to find the velocity of a fluid, the Pitot tube measures pressure and not velocity. The Pitot tube works according to Bernoulli's principle since it gives us pressure.