  # Fluid Mechanics Concepts

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A question pack on fluid mechanics.

Fluid Mechanics Concepts Q18

A flow is considered to be compressible if its Mach number is greater than ______________.

A

0.03

B

0.3

C

5

D

1

Fluid Mechanics Concepts Q16

Transition from a laminar pipe flow to a turbulent flow typically occurs with a Reynolds number in the range of ______________.

A

2,300‑4,000

B

500‑1,000

C

10$^5$ ‑10$^6$

D

50,000‑100,000

Fluid Mechanics Concepts Q17

For a laminar pipe flow, how does the friction factor change when the Reynolds number increases?

A

The friction factor decreases.

B

The friction factor is kept constant.

C

The friction factor increases.

D

None of the above

Fluid Mechanics Concepts Q15

What are the dimensions of surface tension?

A

M L$^{‑1}$

B

M L$^{‑1}$T$^{‑2}$

C

M$^{2}$L$^{‑1}$T

D

M$^{‑1}$T$^{‑2}$

Fluid Mechanics Concepts Q14

What does a barometer measure?

A

Thermal conductivity

B

Wind velocity

C

Atmospheric pressure

D

Relative humidity

Fluid Mechanics Concepts Q13

What does the Froude number measure?

A

The ratio of inertial forces to viscous forces.

B

The ratio of surface tension to inertial forces.

C

The ratio of inertial forces to gravitational forces.

D

The ratio of momentum diffusivity to thermal diffusivity.

Fluid Mechanics Concepts Q12

What does the Reynolds number measure?

A

The ratio of inertial forces ρV$^2$/L to viscous forces μV/L$^2$

B

The ratio of surface tension to inertial forces

C

The ratio of gravitational force to fluid’s inertia

D

The ratio of momentum diffusivity to thermal diffusivity

Fluid Mechanics Concepts Q11

What is a laminar pipe flow?

A

Movement of fluid slowly in layers in a pipe, without much mixing among the layers

B

A flow whose Reynolds number exceeds 2300

C

Movements of fluid are chaotic with significant mixing

D

None of the above

Fluid Mechanics Concepts Q10

What is the pressure on a given object?

A

Pressure is the force divided by the area over which the force is applied.

B

Pressure is equal to surface tension.

C

Pressure is the force times the area over which the force is applied.

D

Pressure is equal to the object’s acceleration times its mass.

Fluid Mechanics Concepts Q9

Which of the following dimensionless numbers is used to compare surface tension against inertial forces?

A

Reynolds number

B

Weber number

C

Prandtl number

D

Froude number

Fluid Mechanics Concepts Q8

Which of the following is a streamline?

A

The locus of points of all the fluid particles that have passed through a given point

B

A family of curves, which are normal to the velocity vector of the flow

C

A family of curves that track the trajectories of fluid particles

D

A family of curves that are instantaneously tangent to the velocity vector of the flow

Fluid Mechanics Concepts Q7

Which of the following is NOT a dimensionless number?

A

Pressure coefficient

B

Mach number M

C

Gas constant R

D

Friction factor f

Fluid Mechanics Concepts Q5

Which of the following is the definition of Froude number?

A

V$^2$/Lg

B

μ VL/ρ

C

VL/σ

D

None of the above

Fluid Mechanics Concepts Q6

Which of the following statement about streamlines is false?

A

Streamlines cannot cross each other.

B

Streamlines provide a snapshot of the entire flow field.

C

Streamlines track trajectories of fluid particles.

D

The tangent at each point on a streamline is the direction of the velocity vector at that point.

Fluid Mechanics Concepts Q4

Which of the following statements about fully developed pipe flows is false?

A

The streamwise velocity component satisfies u$_z$ = 0.

B

“Boundary layers” from opposite sides of the pipe are separated and continue growing.

C

The radial component of the velocity is zero.

D

The entrance length depends on the Reynolds number.

Fluid Mechanics Concepts Q3

Which of the following statements about surface tension is true?

A

Surface tension is responsible for the weight of liquid droplets.

B

Surface tension is measured in forces per unit length or of energy per unit area.

C

Surface tension is responsible for buoyancy

D

None of the above

Fluid Mechanics Concepts Q2

Which of the following statements about the Moody chart is false?

A

In the laminar zone, friction factor decreases as the Reynolds number increases.

B

In the turbulent zone, friction factor increases as the relative roughness (D/ε) increases.

C

Within the zone of complete turbulence, friction factor is independent of Reynolds number.

D

As relative roughness increases, the boundary of the complete turbulence zone shifts to the right.

Fluid Mechanics Concepts Q1

Which of the following statements about viscosity is true?

A

Viscosity of a fluid depends strongly on its temperature.

B

Viscosity measures the friction between the fluid and the wall.

C

Shear stress is independent of viscosity.

D

For a given rate of angular deformation of a fluid, shear stress is inversely proportional to viscosity.

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