Fluid Mechanics And Machinery Set 1

Mechanical Engineering

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This set of Fluid Mechanics and Machinery Multiple Choice Questions & Answers (MCQs) focuses on Fluid Mechanics And Machinery Set 1

Q1 | The specific gravity of a liquid has
  • the same unit as that of mass density
  • the same unit as that of weight density
  • the same unit as that of specific volume
  • no unit
Answer: no unit
Explaination:
the specific gravity of a liquid is the ratio of two similar quantities (densities) which makes it unitless.
Q2 | The specific volume of a liquid is the reciprocal of
  • weight density
  • mass density
  • specific weight
  • specific volume
Answer: mass density
Explaination:
specific volume(v) is defined as the volume(v ) per unit mass(m).
Q3 | Which one of the following is the unit of specific weight?
  • n = m3
  • n = m2
  • n = m
  • n = ms
Answer: n = m3
Explaination:
specific weight(γ) is defined as the weight(w) per unit volume(v ), i.e.,
Q4 | [p] = [m]/[v] = [m] /[L3] = [ML-3].
  • [m1 l-3 t0].
  • [m1 l0 t0].
  • [m0 l-3 t0].
  • [m0 l0 t0].
Answer: [m0 l0 t0].
Explaination:
the specific gravity of a liquid is the ratio of two similar quantities (densities) which makes it dimensionless.
Q5 | Which one of the following is the
  • [m1 l-3 t0].
  • [m-1 l3 t0].
  • [m-1 l-3 t0]. d) [m0 l3 t0].
Answer: [m-1 l3 t0].
Explaination:
specific volume(v) is defined as the volume(v ) per unit mass(m). thus, [v] = [v]/[m] = [l3]/[m] = [m-1l3].
Q6 | the relation between their specific volumes v1 and v2?
  • v1 > v2
  • v1 < v2
  • v1 = v2
  • cannot be determined due to insufficient information.
Answer: v1 < v2
Explaination:
specific volume(v) is defined as the volume(v ) per unit mass(m).
Q7 | mark of one litre and weighed. The weight of the liquid is found to be 6.5 N. The specific weight of the liquid will be
  • 6:5 kn = m3
  • 6:6 kn = m3
  • 6:7 kn = m3
  • 6:8 kn = m3
Answer: 6:5 kn = m3
Explaination:
specific weight(γ) is defined as the weight(w) per unit volume(v ), i.e.,
Q8 | A beaker is filled with a liquid up to the mark of one litre and weighed. The weight of the liquid is found to be 6.5 N. The specific gravity of the liquid will be
  • 0.65
  • 0.66
  • 0.67
  • 0.68
Answer: 0.66
Explaination:
specific gravity(s) of a liquid is defined as the ratio of the density of the liquid(pl) to that of water(pw).
Q9 | mark of one litre and weighed. The weight of the liquid is found to be 6.5 N. The specific volume of the liquid will be
  • 1 l =kg
  • 1:5 l =kg
  • 2 l =kg
  • 2:5 l =kg
Answer: 1:5 l =kg
Explaination:
specific volume(v) is defined as the volume(v ) per unit mass(m). thus,
Q10 | continuity equation is  
  • mass conservation
  • zeroth law of thermodynamics
  • first law of thermodynamics
  • energy conservation
Answer: mass conservation
Explaination:
continuity equation is derived from the mass conservation principle. it states that for an isolated system, the mass of the system must remain constant.
Q11 | equation of mass conservation into the conservative integral form, which of these theorems is used?
  • stokes theorem
  • kelvin-stokes theorem
  • gauss-siedel theorem
  • gauss divergence theorem
Answer: gauss divergence theorem
Explaination:
the expansion of non- conservative integral equation gives two volume integral terms. one of these terms representing the mass flow is converted into surface integral using the gauss divergence theorem.
Q12 | ρV→. dS→ is positive when  
  • the mass flow is outward
  • the mass flow is inward
  • the mass flow is positive
  • the mass flow is negative
Answer: the mass flow is outward
Explaination:
ds→ always points outwards to the control volume. so, the product ρv→. ds→ is positive when the mass flow is outwards.
Q13 | Hydraulic gradient line takes into consideration
  • potential and kinetic heads only
  • potential and pressure heads only
  • kinetic and pressure heads only
  • potential, kinetic and pressure heads
Answer: potential and pressure heads only
Explaination:
hgl is obtained by plotting piezometric head at various points along the axis of the pipe.
Q14 | Which of the following is true?
  • egl always drops in the direction of c
  • egl always rises in the direction of flow
  • egl always remains constant in the direction of flow
  • egl may or may not in the direction of flow
Answer: egl always drops in the direction of c
Explaination:
egl is obtained by plotting total head at various points along the axis of the pipe. since the total head decreases in the direction of flow, egl will always drop in that direction.
Q15 | Which of the following is true?
  • hgl always drops in the direction of flow
  • hgl always rises in the direction of flow
  • hgl always remains constant in the direction of flow
  • hgl may or may not in the direction of flow
Answer: hgl may or may not in the direction of flow
Explaination:
hgl is obtained by plotting piezometric head at various points along the axis of the pipe. since pressure may either rise or fall in the direction of flow, hgl may or may not change in that direction.
Q16 | Which of the following is true?
  • hgl will never be above egl
  • hgl will never be under egl
  • hgl will never coincide with egl
  • hgl will may or may not be above egl
Answer: hgl will never be above egl
Explaination:
egl is obtained by plotting total head and hgl is obtained by plotting piezometric head at various points along the axis of the pipe.
Q17 | The vertical intercept between EGL and HGL is equal to
  • pressure head
  • potential head
  • kinetic head
  • piezometric head
Answer: kinetic head
Explaination:
egl is obtained by plotting
Q18 | The slope of HGL will be
  • greater than that of egl for a pipe of uniform cross-section
  • smaller than that of egl for a pipe of uniform cross-section
  • equal than that of egl for a pipe of uniform cross-section
  • independent of that of egl for a pipe of uniform cross-section
Answer: equal than that of egl for a pipe of uniform cross-section
Explaination:
the vertical intercept between egl and hgl is equal to the kinetic head. for a pipe of uniform cross-section, there will be no change in the velocity of flow across
Q19 | For a nozzle, the vertical intercept between EGL and HGL
  • increases
  • decreases
  • remains constant
  • may increase or decrease
Answer: increases
Explaination:
the vertical intercept between egl and hgl is equal to the kinetic head. for a nozzle, the cross-sectional area decreases in the direction of flow leading to
Q20 | between EGL and HGL
  • increases
  • decreases
  • remains constant
  • may increase or decrease
Answer: decreases
Explaination:
the vertical intercept between egl and hgl is equal to the kinetic head. for a diffuser, the cross-sectional area increases in the direction of flow leading to a decrease in the velocity of flow across the pipe. since the kinetic head decreases, the vertical intercept between egl and hgl will decrease.
Q21 | Which of the following is true?
  • the slope of egl will always be greater than that of the axis of the pipe
  • the slope of egl will always be smaller than that of the axis of the pipe
  • the slope of egl will always be equal to that of the axis of the pipe
  • the slope of egl will always be independent of that of the axis of the pipe
Answer: the slope of egl will always be independent of that of the axis of the pipe
Explaination:
egl is obtained by plotting total head at various points along the axis of the pipe.
Q22 | the pressure vary with the length of the pipe?
  • linearly
  • parabolic
  • exponential
  • constant
Answer: linearly
Explaination:
in a zero acceleration fully- developed flow in a pipe, the pressure gradually decreases linearly along the length of the pipe. hence, the pressure variation is said to be linear.
Q23 | When a problem states “The velocity of the water flow in a pipe is 20 m/s”, which of the following velocities is it talking about?
  • rms velocity
  • average velocity
  • absolute velocity
  • relative velocity
Answer: average velocity
Explaination:
in a pipe-flow, the velocity is always referred to the average velocity. there may be a case where all water particles move in the same direction with 20 m/s, then the average velocity will be equal to absolute velocity. but, this is only a special case.
Q24 | Which of the factors primarily decide whether the flow in a circular pipe is laminar or turbulent?
  • the prandtl number
  • the pressure gradient along the length of the pipe
  • the dynamic viscosity coefficient
  • the reynolds number
Answer: the reynolds number
Explaination:
high reynolds number flows
Q25 | How is Reynolds number defined as?
  • ratio of pressures in the inlet to the outlet of a pipe
  • the product of velocity of the flow and the diameter of the pipe, divided by the kinematic viscosity of fluid
  • the product of density of the fluid, velocity of the flow and the diameter of the pipe, divided by the dynamic viscosity of fluid
  • ratio of inertia force to viscous force
Answer: ratio of inertia force to viscous force
Explaination:
the question demands the definition and not the commonly used formula of reynolds number. some of them denote the formula of reynolds number. the definition of reynolds number is the ratio of inertia force to viscous force in a pipe flow.
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