Fluid Mechanics Sheet 26

1) Question.

A circular plate of diameter d is submerged in water vertically, so that the topmost point is just at the water surface. The centre of pressure on the plate will be below the water surface at a depth of
Answer.
- 1
  
  $\frac{5 d}{8}$
- 2
  
  $\frac{2 d}{3}$
- 3
  
  $\frac{11 d}{16}$
- 4
  
  $\frac{3 d}{4}$
Answer: 1

Explanation:
2) Question.

A racing car with a partially filled fuel tank moves in the horizontal direction at a uniform acceleration equal to g. The free surface of the liquid fuel in the tank will assume a slope of
Answer.
- 1
  
  $20^{0}$
- 2
  
  $30^{0}$
- 3
  
  $45^{0}$
- 4
  
  $60^{0}$
Answer: 3

Explanation:
3) Question.
Consider the following fluids:
1. Blood
2. Glycerine
3. Molasses
4. Slurry of clay in water
5. Kerosene
Among these, non-Newtonian fluids would include
Answer.
- 1
  
  2,4 and 5
- 2
  
  2,3 and 4
- 3
  
  1,3 and 4
- 4
  
  1,4 and 5
Answer: 3

Explanation:
4) Question.

Which one of the following pairs of situations and types of water surface profiles is not correctly matched?
Answer.
- 1
  
  Mild slope; flow over free overall: $M_{2}$
- 2
  
  Mild slope; flow downstream of a sluice gate: $M_{1}$
- 3
  
  Critical slope; flow downstream of a sluice gate: $C_{3}$
- 4
  
  Critical slope; flow behind an overflow weir: $C_{1}$
Answer: 2

Explanation:
5) Question.

Which one of the following pairs of types of flow and situations is not correctly matched?
Answer.
- 1
  
  Non-uniform flow... velocity changes magnitude with distance
- 2
  
  Uniform flow... flow in a channel bend
- 3
  
  Steady flow... velocity does not change with time
- 4
  
  Tranquil flow... Froude number of flow is less than 1
Answer: 2

Explanation:
6) Question.

Which one of the following statements is not correct?
Answer.
- 1
  
  Water hammer occurs in a situation when there is unsteady flow in a pipe.
- 2
  
  Fall of pressure due to decrease in velocity results in the phenomenon of water hammer.
- 3
  
  Propagation of high pressure through elastic media gives rise to water hammer.
- 4
  
  For water hammer to develop, the valve at the end of a pipeline must be fully closed.
Answer: 2

Explanation:
7) Question.

Which one of the following statements is not correct?
Answer.
- 1
  
  In the study of flow between two fixed parallel plates, the flow is assumed two dimensional.
- 2
  
  In flow between parallel plates, if the distance between the plates and the viscosity remains constant, then the pressure gradient is also constant provided that the flow is steady.
- 3
  
  Velocity distribution for laminar flow between two parallel plates shows that velocity varies directly with pressure gradient.
- 4
  
  In case of flow between parallel plates, variation of shear is linear.
Answer: 2

Explanation:
8) Question.
Consider the following statements :
1. In a source, equipotential lines are circles.
2. Flownet is a representation of 2-dimensional irrotational flow of incompressible fluid.
3. Boundaries act as limiting equipotential lines in a flow net.
4. In uniform flow region, streamlines will be parallel and equidistant.
Of these statements
Answer.
- 1
  
  1,2 and 3 are correct
- 2
  
  1,2 and 4 are correct
- 3
  
  2,3 and 4 are correct
- 4
  
  1,3 and 4 are correct
Answer: 2

Explanation:
9) Question.

Which one of the following statements is not correct ?
Answer.
- 1
  
  In free vortex flow, streamlines are concentric spirals and flow continuously circles the origin.
- 2
  
  In free vortex flow, the flow velocity is in tangential direction only and varies inversely as the distance from the origin.
- 3
  
  In a free vortex, flow is rotational at the core and irrotational away from it.
- 4
  
  In a forced vortex, flow is rotational, that is, fluid particles undergo rotation about their mass centre.
Answer: 1

Explanation:
10) Question.
Consider the following statements relating hydrostatic forces on submerged surface :
1. The pressure centre is always below the centroid of any plane submerged surface that is not horizontal.
2. Total force on a curved surface is the product of the average force and the submerged area.
3. The magnitude of hydrostatic pressure at a particular depth is a function of the shape of the surface.
4. The vertical component of force on a body completely submerged in a static reservoir of fluid is equal to the weight of the fluid displaced by the body.
Of these statements
Answer.
- 1
  
  1,2 and 3 are correct
- 2
  
  2,3 and 4 are correct
- 3
  
  1,3 and 4 are correct
- 4
  
  1,2 and 4 are correct
Answer: 4

Explanation:
11) Question.
Consider the following statements relating to some fluid properties :
1. The variation of kinematic viscosity between liquids and gases is much less than the variation of dynamic viscosity.
2. Surface energy is caused by relative forces of cohesion and adhesion between the fluids.
3. Mercury possesses larger vapour pressure than benzene and hence benzene is more volatile.
4. Bulk modulus of water is 3,00,000 units and that of gas is 15 units. This indicates that gas is 20,000 times more compressible than water.
Of these statement
Answer.
- 1
  
  1,2 and 3 are correct
- 2
  
  1,2 and 4 are correct
- 3
  
  2,3 and 4 are correct
- 4
  
  1,3 and 4 are correct
Answer: 2

Explanation:
12) Question.

Glycerine (specific weight $1260 k g / m^{3}$ , dynamic viscosity $8.00 \times 10^{- 2} k g - s e c / m^{2}$ ) is spread freely to a thickness of 1 mm between a bottom stationary plate and a top moveable plate of $10 c m^{2}$ area. The top plate is to be moved at a uniform speed of 1 m/s. The fo
Answer.
- 1
  
  1.6 kg
- 2
  
  0.8 kg
- 3
  
  0.16 kg
- 4
  
  0.08 kg
Answer: 4

Explanation:
13) Question.

In order that a droplet of water at $20^{0} C$ $(σ = 0.0728 N / m)$ has an internal pressure 1 kPa greater than that outside it, its diameter should be nearly
Answer.
- 1
  
  0.15 mm
- 2
  
  0.3 mm
- 3
  
  0.6 mm
- 4
  
  1.2 mm
Answer: 2

Explanation:
14) Question.

Flow of air can be considered to be incompressible within 1% error if the Mach Number of flow is less than
Answer.
- 1
  
  0.1
- 2
  
  0.2
- 3
  
  0.4
- 4
  
  0.6
Answer: 2

Explanation:
15) Question.

Considering that $\frac{P}{ρ^{k}}$ = constant expresses an isentropic process, which one of the following is not a representation of speed of a sound wave ?

(Symbols have the usual meaning)
Answer.
- 1
  
  $\sqrt{k g R T}$
- 2
  
  $\sqrt{\frac{d p}{d ρ}}$
- 3
  
  $\sqrt{\frac{K}{ρ}}$
- 4
  
  $\sqrt{\frac{p}{ρ}}$
Answer: 1

Explanation:
16) Question.

A velocity field with no components in the y and z directions is given by $V = 6 + 2 x y + r^{2}$

The accelaration along the x-direction at a point (3,1,2) at time 2, is
Answer.
- 1
  
  8 units
- 2
  
  16 units
- 3
  
  28 units
- 4
  
  36 units
Answer: 4

Explanation:
17) Question.
Consider the following types of weirs :
1. Proportional weir
2. Cipolletti weir
3. Parabolic weir
4. Rectangular weir (without end treatment)
All these weirs have varying values exponent in the formula $Q = K H^{n}$ . The correct sequence of these weirs in increasing order of the value of 'n' is
Answer.
- 1
  
  2,1,3,4
- 2
  
  2,1,4,3
- 3
  
  1,2,3,4
- 4
  
  1,2,4,3
Answer: 4

Explanation:
18) Question.

In a horizontally held injection syringe, the piston of $0.2 c m^{2}$ cross-sectional area is pushed at a constant speed of 1.0 cm/s to eject water into the atmosphere through a hypodermic needle of $0.7 m m^{2}$ cross sectional area while rinsing. Neglecting losses, the force required to move the piston is nearly
Answer.
- 1
  
  6 kg
- 2
  
  $6 \times 10^{- 3} k g$
- 3
  
  $6 \times 10^{- 5} k g$
- 4
  
  $6 \times 10^{- 7} k g$
Answer: 1

Explanation:
19) Question.

A hollow cylinder made of wood (sp.gr. = 0.8) has an external diameter of 1.0 m and an internal diameter of 0.6 m. It floats in water with its axis vertical and is in stable equilibrium. This is possible only when the length of the cylinder is equal to or less than
Answer.
- 1
  
  0.72 m
- 2
  
  0.95 m
- 3
  
  1.03 m
- 4
  
  1.20 m
Answer: 3

Explanation:
20) Question.
Consider the following statements relating to hydraulic gradient line and energy gradient line :
1. In the case of a fluid flowing in a pipeline, hydraulic gradient line and energy gradient line may coincide.
2. The line joining the points representing piezometric heads is known as hydraulic gradient.
3. In the case of ideal fluid, energy gradient line is always horizontal.
4. Hydraulic gradient line has a downward slope in the case of flow through pipes.
Of these statement
Answer.
- 1
  
  1,2 and 3 are correct
- 2
  
  1,3 and 4 are correct
- 3
  
  2,3 and 4 are correct
- 4
  
  1,2 and 4 are correct
Answer: 3

Explanation:

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