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Fluid Mechanics - 2

20 Questions MCQ Test Mock Test Series for SSC JE Mechanical Engineering | Fluid Mechanics - 2

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Attempt Fluid Mechanics - 2 | 20 questions in 12 minutes | Mock test for SSC preparation | Free important questions MCQ to study Mock Test Series for SSC JE Mechanical Engineering for SSC Exam | Download free PDF with solutions

QUESTION: 1

In a flow field, at the stagnation point _______.

A.
Pressure is zero
B.
Velocity of fluid is zero
C.
Pressure head is equal to velocity
D.
None of these

Solution:

A stagnation point is a point in a flow field where the local velocity of the fluid is zero. The Bernoulli equation shows that the static pressure is highest when the velocity is zero and hence static pressure is at its maximum value at stagnation points. This static pressure is called the stagnation pressure.

QUESTION: 2

The number of π parameters needed to express the function F(A, V, t μ, L) = 0 are

A.
5
B.
4
C.
3
D.
2

Solution:

Total no of π terms = m - n

Here, m = total parameter = 5

n = fluid property, flow property and geometric property (ν, v, L) = 3

∴ no of π – terms = 5 – 3 = 2

QUESTION: 3

If the particles of a fluid attain such velocities that vary from point to point in magnitude and direction as well as from instant, the flow is _______.

A.
Uniform flow
B.
Steady flow
C.
Turbulent flow
D.
Laminar flow

Solution:

In fluid dynamics, turbulent flow is characterized by the irregular movement of particles of the fluid. In contrast to laminar flow the fluid does not flow in parallel layers, the lateral mixing is very high, and there is a disruption between the layers. In turbulent flow the speed of the fluid at a point is continuously undergoing changes in both magnitude and direction.

QUESTION: 4

The relation for an irrotational flow is known as which one of the following?

A.
Navier – Stokes equation
B.
Laplace equation
C.
Reynolds equation
D.
Euler’s equation

Solution:

For three dimensional steady incompressible flow the continuity equation is

Which is nothing but Δ²ϕ = 0. The “Laplace equation“. Thus any function that satisfied Laplace equation is a possible case of fluid flow.

QUESTION: 5

The flow in a pipe is turbulent when Reynold number is

A.
Less than 2000
B.
Between 2000 and 2800
C.
More than 4000
D.
None of these

Solution:

The flow in a circular pipe is

Laminar Flow: Re ≤ 2300

Transitional flow: 2300 ≤ Re ≤ 4000

Turbulent flow: Re ≥ 4000

QUESTION: 6

Kinematic viscosity of water in comparison to mercury is _____.

A.
Higher
B.
Lower
C.
Same
D.
Higher/lower depending on temperature

Solution:

The dynamic viscosity of mercury (1.52 cp) is greater than water (0.894 cp). The kinematic viscosity is the dynamic viscosity divided by the density. Mercury is a lot denser than water, so its kinematic viscosity is lower than the kinematic viscosity of water.

QUESTION: 7

Dynamic viscosity of water in comparison to mercury is

A.
Higher
B.
Lower
C.
Same
D.
Unpredictable

Solution:

Dynamic viscosity of water at 20°C

= 1.005 centipoise

Dynamic viscosity of mercury at 20°C

= 1.6 centipoise

QUESTION: 8

According to newton’s low of viscosity, the shear is directly proportional to:

A.
dx/dy
B.
Μdv/dy
C.
dx/dt
D.
dv/dy

Solution:

Hence shear stress is proportional to velocity gradient.

QUESTION: 9

A fluid of kinematic viscosity 0.5 cm²/sec flows through a 10 cm diameter pipe, The maximum average velocity for laminar flow will be

A.
less than 1 m/sec
B.
1 m/sec
C.
1.5 m/sec
D.
2 m/sec

Solution:

Maximum Reynolds’s number for laminar flow = 2000

We know that, RE=

∴Maximumvelocity

QUESTION: 10

Metacentre is the point of intersection of

A.
vertical upward force through c.g. of body and center line of body
B.
buoyant force and the center line of body
C.
mid - point between c.g. and center of buoyancy
D.
All of these

Solution:

The point ' M ' at which the line of action of the new buoyant force intersects the original vertical through the CG of the body, is called the metacentre. It is a point about which a floating body starts oscillating, when given a small angular displacement.

GM > 0 (M is above G) Stable equilibrium

GM = 0 (M coinciding with G) Neutral equilibrium

GM < 0 (M is below G) Unstable equilibrium

QUESTION: 11

The density of air at 10° C and 1 MPa abs, in SI units is

A.
1.231
B.
12.31
C.
118.4
D.
65.0

Solution:

Density (ρ)=

QUESTION: 12

A centrifugal pump delivers a liquid when pressure rise in impeller is equal to _______

A.
Kinetic head
B.
Velocity head
C.
Static head
D.
Manometric head

Solution:

Manometric head is the head against which head is required to be produced by the pump to deliver water to the destination. Manometric head is higher than the sum of suction and delivery heads because it accounts for head losses due to friction.

QUESTION: 13

Separation of flow occurs when pressure gradient

A.
tends to approach zero
B.
becomes negative
C.
reduces to a value when vapor formation starts
D.
None of these

Solution:

Flow separation occurs when the pressure gradient is positive and velocity gradient is negative.

QUESTION: 14

The correct relationship among displacement thickness ‘d’, momentum thickness ‘m’ and energy thickness 'e' is

A.
d > m > e
B.
d > e > m
C.
e > m > d
D.
e > d > m

Solution:

Displacement thickness,

Momentum thickness,

Energy thickness,

δ > δ_E > δ_θ

QUESTION: 15

Bernoulli’s equation is applied to

A.
Venturimeter
B.
Orifice meter
C.
Pitot tube meter
D.
All of the above

Solution:

Bernoulli's equation states that the summation of pressure head, kinetic head and datum/potential head is constant for steady, incompressible, irrotational and non-viscous flow. In other words an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy i.e. the total energy of a flowing system remain constant until external force is applied. So Bernoulli’s equation refers to conservation of energy.

All flow measuring devices like Venturimeter, Orifice meter, Pitot tube meter works on the Bernoulli’s theorem.

QUESTION: 16

Pascal second is the unit of

A.
Pressure
B.
Kinematic viscosity
C.
Dynamic viscosit
D.
Surface tension

Solution:

Dynamic viscosity (μ)

μ = Pa – S

QUESTION: 17

Spherical shape of droplets of mercury is due to:

A.
High density
B.
High surface tension
C.
High adhesion
D.
Water

Solution:

Surface tension is responsible for spherical shape of droplets. Surface tension for mercury is 0.485 N/m and that for water is 0.072 N/m.

QUESTION: 18

A stream function is given by (x² – y²). The potential function of the flow will be

A.
2xy + f(x)
B.
2(x² – y²)
C.
-2xy + constant
D.
2xy + f(y)

Solution:

Stream function Ψ = x² – y²

Φ = -2xy + C

QUESTION: 19

An accumulator is a device to store

A.
Sufficient quantity of liquid to compensate the change in discharge
B.
Sufficient energy to derive the machine when the normal energy source does not function
C.
Sufficient energy in case of machines which work intermittently to supplement the discharge from the normal source
D.
Liquid which otherwise would have gone to waste

Solution:

An accumulator is a device to store sufficient energy in case of machines which work intermittently to supplement the discharge from the normal source.

QUESTION: 20

In case of power transmission through pipes, maximum efficiency is