JSSC- JE Mechanical Engg. Question Bank (Chapter – 13)

Mechanical

Which equation is used to describe the energy conservation of an ideal fluid flowing steadily along a streamline?

• Continuity equation
• Bernoulli’s equation
• Newton’s law of viscosity
• Pascal’s law

Explanation:

• Bernoulli’s equation is based on the conservation of mechanical energy for an ideal fluid flowing steadily along a streamline.
• For an ideal fluid, the flow is assumed to be incompressible and non-viscous.

Which of the following is the standard form of Bernoulli’s equation in terms of head?

• p/ρg + V²/g + z = constant
• p/ρg + V²/2g + z = constant
• p/ρg + V²/2 + gz = constant
• p/ρ + V²/2g + z = constant

Explanation:

• Bernoulli’s equation in head form is:
• p/ρg + V²/2g + z = constant
• Here, p/ρg is pressure head, V²/2g is velocity head, and z is elevation head.

Bernoulli’s equation is fundamentally based on which principle?

• Conservation of mass
• Conservation of momentum
• Conservation of energy
• Conservation of angular momentum

Explanation:

• Bernoulli’s equation represents conservation of mechanical energy per unit weight of fluid.
• The three main forms of energy are pressure energy, kinetic energy and potential energy.

What is the pressure head of a flowing fluid?

• V²/2g
• z
• p/ρg
• ρg/p

Explanation:

• Pressure head represents pressure energy per unit weight of fluid.
• Pressure head = p/ρg, where p is pressure, ρ is density and g is acceleration due to gravity.
• Its unit is metre of fluid.

What is meant by velocity head?

• p/ρg
• z
• V²/2g
• V/g

Explanation:

• Velocity head represents kinetic energy per unit weight of fluid.
• Velocity head = V²/2g.
• It is expressed in metres of fluid.

What is elevation head in Bernoulli’s equation?

• p/ρg
• V²/2g
• z
• ρgV

Explanation:

• The elevation head represents the potential energy per unit weight of fluid.
• It is equal to the vertical elevation z measured from a selected datum.

What is the total head of a fluid in Bernoulli’s equation?

• p/ρg + V²/2g
• V²/2g + z
• p/ρg + V²/2g + z
• p/ρ + V²/2 + z

Explanation:

• Total head is the sum of pressure head, velocity head and elevation head.
• Total head = pressure head + velocity head + elevation head.
• Therefore, H = p/ρg + V²/2g + z.

What is the unit of total head in Bernoulli’s equation?

• Pa
• N
• J/kg
• m of fluid

Explanation:

• When Bernoulli’s equation is expressed in head form, each energy term is divided by g.
• Therefore, pressure head, velocity head, elevation head and total head are expressed in metres of fluid.

For an ideal fluid flowing steadily along a streamline, the total head is:

• Always increasing
• Always decreasing
• Constant
• Zero

Explanation:

• For steady, incompressible, inviscid flow along a streamline with no pump, turbine or other energy interaction, Bernoulli’s equation gives a constant total head.

Which of the following assumptions is associated with the ideal-fluid form of Bernoulli’s equation?

• Highly viscous flow
• Compressible flow with large density changes
• Inviscid and incompressible flow
• Unsteady flow with large energy losses

Explanation:

• The basic Bernoulli equation assumes steady flow, incompressible fluid, negligible viscosity and application along a streamline.
• For flow between different streamlines, additional conditions are required, such as irrotational flow.

In a horizontal pipe of varying cross-section carrying an ideal incompressible fluid, if the velocity increases, the static pressure generally:

• Increases
• Decreases
• Remains unchanged
• Becomes zero

Explanation:

• For a horizontal pipe, z is constant.
• Therefore, Bernoulli’s equation becomes p/ρg + V²/2g = constant.
• If velocity increases, velocity head increases and static pressure head decreases.

Which principle explains the decrease in pressure when fluid velocity increases in a horizontal ideal-flow passage?

• Pascal’s law
• Newton’s third law
• Bernoulli’s principle
• Archimedes’ principle

Explanation:

• Bernoulli’s principle states that, for steady ideal flow along a streamline, an increase in kinetic energy per unit weight is accompanied by a corresponding decrease in pressure energy when elevation remains constant.

What happens to the velocity of an incompressible fluid when the cross-sectional area of a pipe is reduced?

• Velocity decreases
• Velocity becomes zero
• Velocity increases
• Velocity remains constant for all conditions

Explanation:

• From the continuity equation, Q = AV.
• For constant discharge Q, velocity is inversely proportional to area.
• Therefore, reducing the pipe area increases fluid velocity.

Which equation is commonly used along with Bernoulli’s equation to determine velocity changes in a pipe?

• Gas equation
• Continuity equation
• Newton’s law of cooling
• Fourier’s law

Explanation:

• The continuity equation for steady incompressible flow is Q = AV.
• Bernoulli’s equation gives the energy relationship, while the continuity equation relates velocity to flow area.

Which of the following is an application of Bernoulli’s equation?

• Measurement of viscosity using a viscometer
• Flow measurement using a venturimeter
• Measurement of temperature using a thermometer
• Measurement of mass using a weighing balance

Explanation:

• A venturimeter uses the pressure difference between its inlet and throat to determine fluid discharge.
• Bernoulli’s equation and the continuity equation are used in its analysis.

Which device is primarily used to measure fluid velocity based on Bernoulli’s principle and stagnation pressure?

• Venturimeter
• Orifice meter
• Pitot tube
• Rotameter

Explanation:

• A Pitot tube measures fluid velocity by converting kinetic energy into pressure at a stagnation point.
• For ideal flow, V = √[2(p₀ − p)/ρ].

At the stagnation point of an ideal flow, the fluid velocity is:

• Maximum
• Equal to inlet velocity
• Zero
• Infinite

Explanation:

• A stagnation point is a point where the fluid comes to rest relative to the measuring device.
• Therefore, velocity at the stagnation point is zero and the corresponding pressure is called stagnation pressure.

In a venturimeter, the velocity of fluid is maximum at the:

• Inlet
• Convergent section entrance
• Throat
• Outlet of diffuser

Explanation:

• The throat has the minimum cross-sectional area.
• For incompressible steady flow, Q = AV, so the velocity becomes maximum at the throat.
• The static pressure is correspondingly minimum at the throat under ideal conditions.

Which part of a venturimeter helps recover pressure after the throat?

• Inlet pipe
• Convergent section
• Diffuser
• Throat

Explanation:

• The diffuser is the gradually expanding section after the throat.
• As velocity decreases in the diffuser, part of the kinetic energy is converted back into pressure energy.
• A gradual expansion helps reduce flow separation and energy loss.

Bernoulli’s equation can be applied directly between two points when they lie on:

• Different unrelated flow systems
• The same streamline for the basic steady-flow form
• Different fluids
• Different independent pipes without connection

Explanation:

• The basic Bernoulli equation is applied between two points on the same streamline for steady, incompressible, inviscid flow.
• For irrotational flow, the Bernoulli constant can be the same throughout the flow field.

Which energy term represents the potential energy per unit weight of a fluid?

• Pressure head
• Velocity head
• Elevation head
• Friction head

Explanation:

• Elevation head is z and represents gravitational potential energy per unit weight.
• Pressure head represents pressure energy, while velocity head represents kinetic energy.

Which energy term represents kinetic energy per unit weight in Bernoulli’s equation?

• Pressure head
• Velocity head
• Elevation head
• Datum head

Explanation:

• Kinetic energy per unit mass is V²/2.
• Dividing by g to express energy per unit weight gives the velocity head V²/2g.

Which energy term is represented by p/ρg in Bernoulli’s equation?

• Elevation head
• Velocity head
• Pressure head
• Friction head

Explanation:

• Pressure head is p/ρg.
• It represents the pressure energy available per unit weight of fluid.

If the elevation and pressure heads remain constant in an ideal flow, an increase in velocity head will cause the total head to:

• Increase
• Decrease
• Remain constant only if another energy term decreases correspondingly
• Become zero

Explanation:

• Bernoulli’s equation states that the sum of pressure head, velocity head and elevation head remains constant under the ideal assumptions.
• Therefore, if elevation and pressure heads are both unchanged, velocity head cannot increase without violating the equation.

Which equation correctly represents Bernoulli’s equation between two points 1 and 2 for ideal steady flow?

• p₁/ρg + V₁²/g + z₁ = p₂/ρg + V₂²/g + z₂
• p₁/ρg + V₁²/2g + z₁ = p₂/ρg + V₂²/2g + z₂
• p₁/ρ + V₁²/2 + z₁ = p₂/ρ + V₂²/2 + z₂
• p₁/ρg + V₁²/2 + gz₁ = p₂/ρg + V₂²/2 + gz₂

Explanation:

• The correct head form is:
• p₁/ρg + V₁²/2g + z₁ = p₂/ρg + V₂²/2g + z₂
• All three terms have the dimension of length.

Water flows through a pipe at a velocity of 10 m/s. What is its velocity head approximately? Take g = 9.81 m/s².

• 2.55 m
• 5.10 m
• 10.20 m
• 20.40 m

Explanation:

• Velocity head = V²/2g.
• = 10²/(2 × 9.81) = 100/19.62 ≈ 5.10 m.

Water flows through a horizontal pipe whose diameter decreases from 200 mm to 100 mm. If the velocity at the 200 mm section is 2 m/s, what is the ideal velocity at the 100 mm section?

• 2 m/s
• 4 m/s
• 8 m/s
• 16 m/s

Explanation:

• For incompressible flow, A₁V₁ = A₂V₂.
• Since area is proportional to diameter squared:
• V₂ = (D₁/D₂)²V₁ = (200/100)² × 2 = 8 m/s.

For a horizontal ideal fluid flow through a constant-area pipe, the pressure difference between two sections is:

• Always positive
• Always negative
• Zero
• Infinite

Explanation:

• In a constant-area pipe carrying steady incompressible flow, velocity remains constant.
• For a horizontal ideal flow, elevation is also constant.
• Bernoulli’s equation therefore gives equal static pressures at the two sections.

Which of the following is NOT a basic term in the ideal Bernoulli head equation?

• Pressure head
• Velocity head
• Elevation head
• Friction loss head

Explanation:

• The ideal Bernoulli equation contains pressure head, velocity head and elevation head.
• Friction loss is absent because the ideal-fluid assumption neglects viscosity and associated energy losses.
• For real fluid flow, a head-loss term is added to the energy equation.

Which statement about the total head of an ideal fluid is correct?

• It consists only of pressure head.
• It consists only of velocity head.
• It is the sum of pressure head, velocity head and elevation head.
• It is always equal to velocity head.

Explanation:

• Total head is the total mechanical energy per unit weight of fluid.
• It is given by H = p/ρg + V²/2g + z.