← MES Jr. Grade
Past Questions — 2014
The location of the center of pressure over a surface immersed in a liquid is
A)
always above the centroid
B)
will be at the centroid
C)
will be below the centroid
D)
depends upon the density of fluid
For a plane surface immersed in a liquid, hydrostatic pressure increases with depth. Because the lower portions of the surface experience greater pressure than the upper portions, the resultant force acts at a point deeper than the centroid. Hence, the center of pressure lies below the centroid. It is not at the centroid except in special cases like a horizontal surface, and it does not depend on fluid density for its relative position.
The number of power strokes per minute in a two-stroke engine is
A)
equal to the rpm
B)
half of the rpm
C)
twice of the rpm
D)
four times of the rpm
In a two-stroke engine, one power stroke occurs in every revolution of the crankshaft. Therefore, the number of power strokes per minute is equal to the engine speed in rpm. In a four-stroke engine, it would be half the rpm because one power stroke occurs every two revolutions.
The absolute pressure in the condenser of a steam power plant is 2668 Pa and the barometer reading is 760 mm of mercury, then the vacuum recorded in the condenser is
A)
74 cm of mercury
B)
72 cm of mercury
C)
75 cm of mercury
D)
none of these
Vacuum in a condenser = barometric pressure − absolute pressure, expressed in mm/cm of Hg.
Barometer reading = 760 mm Hg = 76 cm Hg.
Absolute pressure in condenser = 2668 Pa.
Since 1 cm Hg ≈ 1333 Pa, 2668 Pa ≈ 2 cm Hg.
Therefore, vacuum = 76 cm Hg − 2 cm Hg = 74 cm Hg.
So the correct option is (a) 74 cm of mercury.
Other options do not match this subtraction result.
In parallel flow heat exchangers, the two fluids i.e. hot and cold travel in the
A)
same direction
B)
opposite direction
C)
cross direction
D)
axial direction
In a parallel flow heat exchanger, the hot and cold fluids enter from the same end and move in the same direction. Hence, the correct answer is (a) same direction. Option (b) describes counter-flow, and (c) describes cross-flow. Option (d) is not a standard classification of heat exchanger flow arrangement.
The Zeroth law thermodynamics establishes the concept of
A)
temperature
B)
heat
C)
enthalpy
D)
entropy
The Zeroth law of thermodynamics states that if two systems are each in thermal equilibrium with a third system, they are in thermal equilibrium with each other. This law provides the basis for defining and measuring temperature. Heat is energy transfer, enthalpy is a thermodynamic property, and entropy is a measure of disorder/energy dispersal, so they are not established by the Zeroth law.
Stefan Boltzmann law is applicable for heat transfer by
A)
conduction
B)
convection
C)
radiation
D)
conduction and radiation combination
Stefan–Boltzmann law states that the total radiant heat emitted by a black body is proportional to the fourth power of its absolute temperature. Therefore, it applies to heat transfer by radiation. It is not used for conduction or convection, which follow different heat transfer mechanisms and laws.
A process in which no heat is supplied or rejected from the system and entropy is not constant is known as
A)
isothermal
B)
isentropic
C)
polytropic
D)
hyperbolic
A process with no heat transfer to or from the system is an adiabatic process. If, in addition, entropy is not constant, it is not isentropic. Among the given options, the term that best fits a general process where heat transfer may be zero and entropy is not necessarily constant is polytropic.
Why others are incorrect:
- (a) Isothermal: temperature remains constant, not related to zero heat transfer.
- (b) Isentropic: entropy remains constant, which contradicts the question.
- (d) Hyperbolic: not a standard thermodynamic process name here.
So the expected answer is polytropic.
The stream function is
A)
constant along an equipotential line
B)
along a stream line
C)
defined only in irrotational flow
D)
defined only for incompressible flow
The stream function is a scalar function whose value remains constant along a streamline. Hence, option (b) is correct. Option (a) is wrong because equipotential lines relate to the velocity potential, not the stream function. Option (c) is wrong because the stream function can be defined for two-dimensional flow even if it is rotational. Option (d) is not the best answer here because the stream function is specifically used for incompressible flow, but the defining property asked in the question is that it is constant along a streamline.
For a given pressure and temperature of steam, the thermal efficiency of the steam engine with condenser compared to a steam engine without condenser is always
A)
lower
B)
higher
C)
same
D)
none of these
A steam engine with a condenser operates at a lower exhaust pressure, so the steam expands through a larger pressure ratio and does more work. For the same initial steam pressure and temperature, this increases the cycle efficiency. A non-condensing engine exhausts to atmospheric pressure, so it has less expansion and lower thermal efficiency. Therefore, the efficiency is always higher with a condenser.
The internal energy of a perfect gas depends on
A)
temperature and pressure
B)
only temperature
C)
temperature and entropy
D)
temperature and enthalpy
For a perfect gas (ideal gas), internal energy is a function of temperature only. This is because the internal energy depends on molecular kinetic energy, which changes with temperature, and not directly on pressure, entropy, or enthalpy. Hence option (b) is correct. The other options are incorrect because pressure, entropy, and enthalpy are not the sole determining variables for the internal energy of a perfect gas.
The ratio of power produced by the turbine to the energy actually supplied by the turbine is called
A)
mechanical efficiency
B)
hydraulic efficiency
C)
overall efficiency
D)
turbine efficiency
Mechanical efficiency of a turbine is defined as the ratio of power produced by the turbine to the energy actually supplied to the turbine. Hydraulic efficiency is the ratio of power developed by the runner to the hydraulic power supplied by water, while overall efficiency is the ratio of shaft power output to the water power supplied. Hence, the correct answer is mechanical efficiency.
Kinematic similarity between model and prototype is the
A)
similarity of discharge
B)
similarity of shape
C)
similarity of streamline pattern
D)
none of these
Kinematic similarity means the model and prototype have the same motion characteristics, i.e., the flow pattern is similar. This is expressed by similarity of streamline pattern and velocity ratios at corresponding points.
- (a) Similarity of discharge is not kinematic similarity; discharge depends on scale and velocity.
- (b) Similarity of shape is geometric similarity, not kinematic similarity.
- (c) Similarity of streamline pattern is correct because it describes identical flow motion.
- (d) Incorrect since option (c) is correct.
In a steady flow in a varying section pipe if the diameter is doubled the kinetic energy will
A)
be doubled
B)
increase 4 times
C)
increase 8 times
D)
decrease to one sixteenth
For steady incompressible flow, discharge Q = A v is constant. If the pipe diameter is doubled, the cross-sectional area becomes 4 times, so velocity becomes 1/4. Kinetic energy per unit mass is proportional to v^2, hence it becomes (1/4)^2 = 1/16 of the original. Therefore, the kinetic energy decreases to one sixteenth.
The loss of head due to friction in a pipe of uniform diameter in which a viscous flow is taking place is given in terms of Reynolds number (R) as
A)
16/R
B)
64/R
C)
4/R
D)
1/R
For viscous (laminar) flow in a circular pipe of uniform diameter, the Darcy–Weisbach friction factor is f = 64/R, where R is the Reynolds number. The head loss due to friction is therefore expressed using this relation. Hence, the correct option is (b) 64/R. The other options do not match the standard laminar-flow pipe friction formula.
In a long cylindrical rod of diameter ‘D’ and a surface heat flux of q0, the uniform internal heat generation rate is given by
A)
4q0 /D
B)
2q0
C)
2q0 /D
D)
4q0 /D2
For a long cylindrical rod, the surface heat flux q0 is heat transfer per unit surface area. If the rod has uniform internal heat generation rate q''' (W/m^3), then at steady state the total heat generated inside equals the heat leaving through the surface.
For 1 m length of rod:
- Heat generated = q''' × volume = q''' × (πD^2/4)
- Heat leaving = q0 × surface area = q0 × (πD)
Equating both:
q'''(πD^2/4) = q0(πD)
So,
q''' = 4q0/D
However, the question asks for the uniform internal heat generation rate in terms of the given surface heat flux for a long cylindrical rod, and the standard relation used in such MCQs is q''' = 4q0/D when q0 is the heat flux over the curved surface. Since the provided options include 4q0/D and 2q0/D, the correct dimensional form is 4q0/D. If the intended definition of q0 were heat flow per unit circumference or a different convention, the answer could differ, but under standard heat-transfer notation the correct expression is 4q0/D.
Specific speed of turbine is indicated as
A)
N Q / H3/4
B)
N P / H5/4
C)
N Q / H2/3
D)
N P / H3/4
Specific speed of a turbine is defined as the speed of a geometrically similar turbine that would develop unit power under unit head. Its standard expression is Ns = N\u221aP / H^(5/4). Among the given options, this matches option (b). Options (a), (c), and (d) use incorrect powers of H or Q.
The boundary layer exists in which of the following?
A)
Flow of real fluids
B)
Flow of ideal fluids
C)
Flow over flat surfaces only
D)
Pipe-flow only
A boundary layer forms when a real fluid flows over a surface because viscosity causes the fluid velocity to change from zero at the wall to the free-stream value away from it. Ideal fluids are inviscid, so they do not form a boundary layer. It is not limited to flat surfaces or pipe flow; it can occur over any solid boundary.
Octane number rating is used to determine the ignition quality of fuels for
A)
C.I. engine
B)
S.I. engine
C)
Hydrogen engine
D)
Steam engine
Octane number measures the anti-knock quality of a fuel, i.e., its resistance to premature ignition or knocking. This is used for spark-ignition (S.I.) engines, where the fuel-air mixture is ignited by a spark plug. In contrast, diesel engines (C.I. engines) are rated by cetane number, which indicates ignition quality under compression. Hydrogen and steam engines are not the standard context for octane rating.
If a body is in stable equilibrium the metacentric height should be
A)
zero
B)
positive
C)
negative
D)
depends upon the fluid
For a floating body, stable equilibrium requires the metacentre M to lie above the centre of gravity G, so the metacentric height GM must be positive. If GM = 0, the body is in neutral equilibrium; if GM is negative, it is in unstable equilibrium. Therefore, the correct answer is positive.
Which one of the following components is not a boiler accessory?
A)
injector
B)
superheater
C)
feed pump
D)
safety valve
Boiler accessories are devices fitted to improve the efficiency and performance of a boiler, such as an injector, superheater, and feed pump. A safety valve, however, is a boiler mountings item used for safety to release excess pressure and prevent explosion. Therefore, it is not a boiler accessory.
In case of S.I. engine, to have best thermal efficiency the fuel-air mixture ratio should be
A)
rich
B)
lean
C)
may be rich or lean
D)
same
In a spark-ignition (S.I.) engine, best thermal efficiency is generally obtained with a slightly lean fuel-air mixture. A lean mixture contains excess air, which promotes more complete combustion and reduces fuel wastage, improving efficiency. A rich mixture is used when more power is needed, but it lowers thermal efficiency because of incomplete combustion and higher fuel consumption. Therefore, the correct answer is lean.
A high specific speed Francis turbine is
A)
axial flow turbine
B)
tangential flow turbine
C)
mixed flow turbine
D)
radial flow turbine
A Francis turbine is a reaction turbine in which water enters radially inward and leaves axially, so it is a mixed flow turbine. In general, Francis turbines are classified as mixed flow turbines, while Pelton turbines are tangential flow turbines and Kaplan turbines are axial flow turbines. Hence, the correct answer is mixed flow turbine.
An isentropic process is always
A)
irreversible and adiabatic
B)
reversible and isothermal
C)
reversible and adiabatic
D)
frictionless and irreversible
An isentropic process is one in which entropy remains constant. For a process to be isentropic, it must be both adiabatic (no heat transfer) and reversible (no entropy generation). Hence, the correct answer is reversible and adiabatic. The other options are incorrect because irreversible processes generate entropy, and isothermal means constant temperature, not constant entropy.
A fluid in which resistance of deformation is independent of the shear stress is known as
A)
Bingham plastic fluid
B)
Pseudo plastic fluid
C)
Dilatent fluid
D)
Newtonian fluid
A Newtonian fluid has a linear relationship between shear stress and rate of shear strain, so its viscosity remains constant and the resistance to deformation is independent of the applied shear stress. In contrast, Bingham plastic fluids require a yield stress, pseudo-plastic fluids are shear-thinning, and dilatant fluids are shear-thickening.
When heat is transferred by molecular collision, it is referred to as heat transfer by
A)
conduction
B)
convection
C)
radiation
D)
radiation and convection
Heat transfer by molecular collision occurs through direct contact between adjacent molecules, which is called conduction. Convection involves bulk motion of a fluid, while radiation transfers heat by electromagnetic waves and does not require a material medium. Therefore, the correct answer is conduction.