← MES Jr. Grade
Past Questions
The power transmission capacity of a belt drive due to centrifugal tension
A)
increases
B)
decreases
C)
remains unaffected
D)
none of these
In a belt drive, centrifugal tension increases with belt speed. This centrifugal tension acts equally on both the tight side and slack side, so it does not help in transmitting useful power. Instead, it reduces the effective difference between tight-side tension and slack-side tension available for power transmission. Hence, as centrifugal tension becomes significant, the power transmission capacity of the belt drive decreases.
Why others are incorrect:
- (a) increases: Incorrect, because centrifugal tension does not contribute to useful driving force.
- (c) remains unaffected: Incorrect, because centrifugal effect changes the effective working tensions.
- (d) none of these: Incorrect, since option (b) is correct.
The materials having same elastic properties in all directions are called
A)
ideal materials
B)
uniform materials
C)
isotropic materials
D)
elastic materials
A material that has the same elastic properties in all directions is called an isotropic material. In isotropic materials, properties like Young’s modulus, Poisson’s ratio, and shear modulus do not change with direction.
Why others are incorrect:
(a) Ideal materials is a general term, not specifically for directional equality of elastic properties.
(b) Uniform materials means composition is same throughout, not necessarily same in all directions.
(d) Elastic materials are those that regain original shape after removal of load, but their properties may still vary with direction.
Brinell number of a material is a measure of its
A)
hardness
B)
ductility
C)
rigidity
D)
roughness
The Brinell number (Brinell Hardness Number, BHN) is obtained from the Brinell hardness test, where a hard steel or carbide ball is pressed into the material and the size of the indentation is measured. Therefore, it is a measure of the material’s hardness. Ductility refers to the ability to deform plastically in tension, rigidity refers to resistance to deformation, and roughness refers to surface finish, so options (b), (c), and (d) are incorrect.
The power transmitted by a belt drive is maximum when the ratio of maximum tension in the belt to that of centrifugal tension is
A)
2
B)
3
C)
4
D)
none of these
For maximum power transmitted by a belt, the standard condition is: maximum tension in the belt T = 3 times the centrifugal tension Tc. This is obtained by differentiating the power expression with respect to belt velocity and setting it to zero. Hence, the ratio T/Tc = 3. Therefore, the correct option is (b). Options (a) and (c) do not satisfy the maximum power condition, and (d) is incorrect.
A long column fails by
A)
crushing
B)
tearing
C)
shearing
D)
buckling
A long column does not usually fail by direct crushing because its slenderness makes it unstable under axial load. It fails by lateral deflection, called buckling, at a load lower than the crushing load. Short columns mainly fail by crushing, while tearing and shearing are not the typical failure modes for long columns under axial compression.
Piston and cylinder of a reciprocating steam engine forms a
A)
rolling pair
B)
turning pair
C)
sliding pair
D)
spherical pair
In a reciprocating steam engine, the piston moves to and fro inside the cylinder in a straight line. Since the relative motion between the piston and cylinder is pure sliding, they form a sliding pair.
Why others are incorrect: rolling pair involves rolling motion, turning pair involves rotational motion about a fixed axis, and spherical pair allows angular movement in multiple directions.
Solid length of a helical spring is the product of
A)
total number of coils and wire diameter
B)
active number of coils and wire diameter
C)
pitch and total number of turns
D)
maximum deflection and inactive coils
For a close-coiled helical spring, the solid length is the length of the spring when all the coils are compressed so that they just touch each other. Therefore, solid length = total number of coils × wire diameter, i.e. Ls = n' × d, where n' is the total number of coils and d is the wire diameter. Hence option (a) is correct. Option (b) is incorrect because solid length depends on total coils, not only active coils. Option (c) gives the free length relation idea, not solid length. Option (d) is unrelated to the definition of solid length.
A flexible coupling can be used for
A)
axial misalignment
B)
angular misalignment
C)
both (a) and (b)
D)
can only be used for aligned shaft
Flexible couplings are designed to transmit torque while accommodating small shaft misalignments. These misalignments may be axial (end movement) as well as angular misalignment between the connected shafts. Hence, a flexible coupling can be used for both types. Option (d) is incorrect because aligned shafts generally use rigid couplings, while flexible couplings are specifically meant to tolerate some misalignment. Options (a) and (b) are individually incomplete, so option (c) is correct.
A positive action clutch is
A)
jaw clutch
B)
a single disk friction clutch
C)
a multi disc friction clutch
D)
a cone clutch
A positive action clutch transmits torque by direct mechanical engagement of interlocking parts, without relying on friction. A jaw clutch works by meshing jaws/dogs together, so it is a positive clutch. Single plate, multi-plate, and cone clutches are all friction clutches, which transmit power by frictional force rather than positive engagement.
The ratio of the torsional strength of a hollow shaft to that of a solid shaft of equal length and weight and made of same material is
A)
more than one
B)
less than one
C)
equal to one
D)
none of these
For shafts of equal length, equal weight, and same material, the cross-sectional areas are equal. A hollow shaft places more material away from the center, which increases the polar section modulus and therefore the torque-carrying capacity.
Torsional strength is proportional to polar section modulus Zp = J/R. For the same area, a hollow shaft has larger Zp than a solid shaft. Hence, the hollow shaft can transmit greater torque before reaching the same allowable shear stress.
Therefore, the ratio of torsional strength of hollow shaft to solid shaft is greater than 1.
Why others are incorrect:
- (b) less than one: incorrect, because hollow shafts are stronger in torsion for the same weight.
- (c) equal to one: incorrect, strength is not the same.
- (d) none of these: incorrect, since option (a) is correct.
The most suitable bearing for resisting heavy loads under slow speed is
A)
hydrodynamic bearing
B)
ball bearing
C)
roller bearing
D)
hydrostatic bearing
A hydrostatic bearing is most suitable for resisting heavy loads at slow speed because the load-carrying oil film is created by externally pressurized lubricant, so it does not depend on shaft speed. Hence it can support very heavy loads even at very low or zero speed.
Why others are incorrect:
- Hydrodynamic bearing: develops pressure due to relative motion, so it is not suitable at slow speed.
- Ball bearing: good for moderate loads and higher speeds, but not the best for very heavy loads.
- Roller bearing: carries heavier loads than ball bearings, but for very heavy loads under slow speed, hydrostatic bearing is superior.
Therefore, the correct answer is hydrostatic bearing.
When the relative motion between two elements is completely or successfully constrained, then these two elements form a
A)
mechanism
B)
machine
C)
kinematic pair
D)
none of these
When the relative motion between two elements is completely or successfully constrained, the two elements together are called a kinematic pair. A mechanism is a combination of links arranged to transmit motion, and a machine is a mechanism or collection of mechanisms that transmits and modifies energy. Hence, the correct answer is kinematic pair.
100 kW of power is to be transmitted by each of two separate shafts, made of the same material. Shaft A is turning at 250 rpm and shaft B at 300 rpm. Which shaft must have greater diameter?
A)
A
B)
B
C)
Both will have the same diameter
D)
None of these
For a shaft transmitting power, torque is given by P = 2πNT/60, so T = 60P/(2πN). For the same power, torque is inversely proportional to speed. Therefore, the shaft running at lower speed must transmit higher torque. Shaft A runs at 250 rpm, which is lower than shaft B at 300 rpm, so shaft A carries greater torque. Since shaft diameter depends on the torque it must withstand, shaft A must have the greater diameter. Hence, option (a) A is correct.
In a spur gear the involute profile is generated from
A)
base circle
B)
pitch circle
C)
addendum circle
D)
dedendum circle
In a spur gear, the involute tooth profile is generated by unwinding a taut string from the base circle. The involute curve is defined from the base circle, not from the pitch, addendum, or dedendum circles. The pitch circle is only a reference circle for gear meshing, while the addendum and dedendum circles define the tooth height limits.
Surge tank is provided to protect the
A)
generator
B)
hydraulic turbine
C)
scroll case
D)
penstock
A surge tank is installed in a hydropower system to absorb sudden pressure changes caused by rapid load variations. It protects the penstock from water hammer and excessive pressure rise or drop. Hence, the correct answer is penstock. The generator, turbine, and scroll case are not the primary components protected by a surge tank.
Total heat of a substance is also known as
A)
internal energy
B)
entropy
C)
latent heat
D)
enthalpy
Total heat of a substance is called enthalpy. Enthalpy is defined as H = U + pV, where U is internal energy. It represents the total heat content of a system at constant pressure. Internal energy is only the energy contained within the system, entropy is a measure of disorder, and latent heat is the heat absorbed or released during a change of state.
During adiabatic saturation process on unsaturated air, the parameter which remains constant is
A)
dry bulb temperature
B)
dew point temperature
C)
wet bulb temperature
D)
relative humidity
In an adiabatic saturation process, unsaturated air is brought into contact with water without heat exchange with the surroundings. The process continues until the air becomes saturated, and the temperature that remains constant throughout this idealized process is the wet bulb temperature. Dry bulb temperature changes due to evaporation, dew point temperature is not constant in the process, and relative humidity increases as saturation is approached.
Which of the following does not relate to C.I. engine?
A)
fuel pump
B)
fuel injector
C)
governor
D)
carburettor
A C.I. (Compression Ignition) engine is a diesel engine. It uses a fuel pump, fuel injector, and governor. A carburettor is used in S.I. (Spark Ignition) engines to mix air and fuel before combustion, so it does not relate to a C.I. engine.
Bernoulli’s theorem deals with the law of conservation of
A)
mass
B)
energy
C)
momentum
D)
none of these
Bernoulli’s theorem states that for an ideal fluid flowing steadily, the sum of pressure energy, kinetic energy, and potential energy remains constant along a streamline. Therefore, it is based on the law of conservation of energy. Mass is conserved by the continuity equation, and momentum is related to Newton’s second law, not Bernoulli’s theorem.
Which of the following rotary types is a positive displacement compressor?
A)
radial flow turbo compressor
B)
axial flow turbo compressor
C)
screw type compressor
D)
mixed flow compressor
A positive displacement compressor traps a fixed volume of air and then reduces its volume to increase pressure. A screw type compressor is a rotary positive displacement compressor because air is compressed between rotating helical screws. In contrast, radial flow turbo, axial flow turbo, and mixed flow compressors are dynamic compressors, not positive displacement types.
In fluid modeling of flow pattern around a body submerged in a fluid, the non-dimensional number that has to be kept the same in the model and prototype is
A)
Weber number
B)
Froude number
C)
Mach number
D)
Reynolds number
For flow pattern around a body submerged in a fluid, the dominant force ratio is between inertial and viscous forces. To ensure dynamic similarity between model and prototype, the Reynolds number must be the same in both. Weber number is used when surface tension effects are important, Froude number for gravity-dominated free-surface flows, and Mach number for compressible flows.
Willan’s line is a straight line graph between the rate of steam consumption and
A)
pressure of steam
B)
temperature of steam
C)
indicated horse power
D)
none of these
Willan’s line is the straight-line relationship between steam consumption and indicated power (indicated horse power, IHP) of an engine at constant speed and cut-off. As load increases, steam consumption varies approximately linearly with IHP. It is not a graph with pressure or temperature of steam, so options (a) and (b) are incorrect. Hence, the correct answer is indicated horse power.
The basic job of feed water treatment in boilers is to overcome the problem of
A)
corrosion
B)
scaling
C)
carry over
D)
all of these
Feed water treatment in boilers is done to remove dissolved salts, gases, and suspended impurities. This helps prevent: corrosion caused by dissolved oxygen and carbon dioxide, scaling caused by hardness salts, and carry over due to foaming and impurities in boiler water. Therefore, the basic job of feed water treatment is to overcome all these problems.
The drag produced by end effects due to the finite length of an aerofoil is known as
A)
profile drag
B)
form drag
C)
induced drag
D)
friction drag
Drag caused by end effects due to the finite span/length of an aerofoil is called induced drag. It arises because pressure differences at the tips create wing-tip vortices, which increase resistance. Profile drag is the sum of skin friction and form drag, form drag is due to shape, and friction drag is due to viscous shear on the surface.
If the head of a turbine is more than 300 m, the type of turbine used should be
A)
Pelton
B)
Kaplan
C)
Francis
D)
Propeller
For very high heads, typically above 300 m, an impulse turbine is preferred. The Pelton turbine is designed for high head and low discharge conditions, so it is the correct choice. Kaplan and propeller turbines are used for low heads, while Francis turbines are suitable for medium heads.