← MES Jr. Grade
Past Questions — 2015
If Young’s modulus of a material is given as 1.2×105 N/mm2 and Bulk modulus is 0.8×105 N/mm2, then Poisson’s ratio of the material is
A)
0.25
B)
0.45
C)
0.65
D)
0.85
Use the relation between Young’s modulus (E), Bulk modulus (K), and Poisson’s ratio (μ): E = 3K(1 − 2μ). Given E = 1.2×10^5 N/mm² and K = 0.8×10^5 N/mm². Substitute: 1.2×10^5 = 3 × 0.8×10^5 × (1 − 2μ). So, 1.2 = 2.4(1 − 2μ). Hence, (1 − 2μ) = 1.2/2.4 = 0.5. Therefore, 2μ = 0.5 and μ = 0.25. So the correct answer is option (a).
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.
Which of the following is a lower pair?
A)
automobile steering gear
B)
ball and roller bearing
C)
cam and follower
D)
belt and chain drives
A lower pair is a kinematic pair in which the two elements have surface contact during relative motion. In ball and roller bearings, the rolling elements and races form constrained surface contact, so they are treated as a lower pair in standard machine theory classification.
Why others are not correct:
- (a) automobile steering gear: generally involves higher-pair type tooth contact between gear elements.
- (c) cam and follower: this is a classic higher pair because the contact is point or line contact.
- (d) belt and chain drives: these are not lower pairs; they involve flexible elements transmitting motion, not a lower kinematic pair.
Hence, the correct answer is ball and roller bearing.
Columns which fail by direct stress only are called
A)
short column
B)
medium column
C)
weak column
D)
long column
A short column fails primarily by crushing due to direct compressive stress, with negligible buckling effect. Medium columns fail by a combination of direct stress and buckling, while long columns fail mainly by buckling. Therefore, the correct answer is short column.
If a material expands freely due to heating it will develop
A)
thermal stress
B)
tensile stress
C)
bending stress
D)
no stress
When a material is heated, it tends to expand. Stress develops only if this expansion is restrained or prevented. If the material is allowed to expand freely, no resisting force is produced, so no thermal stress develops. Hence option (d) is correct. Options (a), (b), and (c) are incorrect because thermal, tensile, or bending stresses arise only when there is some form of constraint or loading.
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.
If a rectangular beam is loaded transversely maximum stress develops at
A)
neutral layer
B)
bottom layer
C)
middle layer
D)
top layer
In a rectangular beam subjected to transverse loading, bending stress varies linearly from zero at the neutral axis to maximum at the extreme outer fibres. Thus, the maximum stress develops at the top and bottom layers, not at the middle or neutral layer. Since only one option is to be chosen and the bottom layer is one of the extreme fibres, the correct option is (b).
Why others are incorrect:
(a) Neutral layer: stress is zero here.
(c) Middle layer: same as near neutral axis, not maximum.
(d) Top layer: also an extreme fibre, but in usual single-answer convention for a sagging beam, bottom layer has maximum tensile stress.
The sleeve or muff of a sleeve coupling is designed by treating it as a
A)
thin pressure vessel
B)
thick pressure vessel
C)
solid shaft
D)
hollow shaft
In a sleeve (muff) coupling, the muff is the outer cylindrical member that fits over the two shafts and transmits torque through the key. For design, the sleeve is treated as a hollow shaft because it is subjected to torsion and has an inner diameter equal to the shaft diameter and an outer diameter equal to the muff diameter.
Why others are incorrect:
(a) thin pressure vessel and (b) thick pressure vessel are pressure-containing members, which is not the case here.
(c) solid shaft is incorrect because the muff has a hollow section, not a solid one.
Material which absorbs large amount of energy is called
A)
hard
B)
tough
C)
brittle
D)
malleable
A material that can absorb a large amount of energy before fracture is called tough. Toughness is the ability of a material to withstand shock and absorb energy up to failure.
Why others are incorrect:
(a) Hard: resists indentation or scratching, not energy absorption.
(c) Brittle: fractures with little deformation and absorbs very little energy.
(d) Malleable: can be hammered into thin sheets, which relates to plastic deformation under compression, not energy absorption.
The energy absorbed in a body, when it is strained within the elastic limits, is known as
A)
strain energy
B)
resilience
C)
modulus of resilience
D)
none of these
When a body is deformed within its elastic limit, the work done on it is stored in the body as internal energy called strain energy.
Why others are incorrect:
- Resilience is the property of a material to absorb energy within the elastic limit and release it on unloading.
- Modulus of resilience is the maximum strain energy stored per unit volume up to the elastic limit.
- Hence, the direct name of the energy absorbed is strain energy.
In case of a thin cylinder the ratio of longitudinal stress to hoop stress is
A)
1/4
B)
4
C)
1/2
D)
2
For a thin cylindrical pressure vessel, hoop stress = pd/2t and longitudinal stress = pd/4t, where p = internal pressure, d = diameter, and t = thickness. Therefore, the ratio of longitudinal stress to hoop stress = (pd/4t) / (pd/2t) = 1/2. Hence option (c) is correct. Options (a), (b), and (d) are incorrect because they do not match the standard stress relations for thin cylinders.
The primary unbalance force in reciprocating masses is
A)
directly proportional to crank radius
B)
directly proportional to square of crank radius
C)
inversely proportional to crank radius
D)
independent of crank radius
The primary unbalance force of a reciprocating mass is given by:
F_p = m \omega^2 r \cos\theta
where m = reciprocating mass, \omega = angular speed, r = crank radius, and \theta = crank angle.
Since F_p is directly proportional to r, the correct option is (a).
Why others are incorrect:
- (b) It is not proportional to r^2; only one power of r appears in the primary force expression.
- (c) It is not inversely proportional to r.
- (d) It is not independent of r because crank radius explicitly appears in the formula.
Whitworth quick return mechanism is an inversion of
A)
four bar chain
B)
single slider crank mechanism
C)
five bar chain
D)
double slider crank mechanism
Whitworth quick return mechanism is obtained as an inversion of the single slider crank chain (mechanism). In this mechanism, the cutting stroke and return stroke take unequal times, giving the quick return effect.
Why others are incorrect:
- (a) Four bar chain: gives mechanisms like crank-rocker, not Whitworth quick return.
- (c) Five bar chain: not the standard parent chain for this mechanism.
- (d) Double slider crank mechanism: gives inversions like elliptical trammel and Oldham coupling.
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.
Which of the following is a spring loaded type governor?
A)
Watt governor
B)
Porter governor
C)
Proell governor
D)
Hartnell governor
A spring-loaded governor uses a spring to provide the controlling force instead of relying only on gravity. Hartnell governor is a spring-loaded centrifugal governor. Watt, Porter, and Proell governors are gravity-controlled governors. Therefore, the correct answer is Hartnell governor.
If the particles of a body vibrate parallel to the axis of the body, then the body is said to have
A)
transverse vibration
B)
torsional vibration
C)
longitudinal vibration
D)
none of these
When particles of a body move to and fro parallel to the axis of the body, the vibration is called longitudinal vibration. In transverse vibration, particles move perpendicular to the axis. In torsional vibration, the body twists about its axis. Therefore, option (c) is correct.
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 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.
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.
Corioli’s component is encountered in
A)
quick return mechanism of shaper
B)
four bar chain mechanism
C)
slider crank mechanism
D)
all of these
Coriolis component of acceleration appears when a point/sliding element moves along a link that is itself rotating. In the quick return mechanism of a shaper, the slider moves along the rotating slotted lever, so Coriolis acceleration is present. In an ordinary four-bar chain and a simple slider-crank mechanism, this specific combination of sliding on a rotating link does not normally occur. Therefore, option (a) is correct, while (b), (c), and (d) are incorrect.
Euler’s formula is applicable for determining the buckling load for
A)
long columns
B)
intermediate columns
C)
medium size columns
D)
short columns
Euler’s buckling formula is valid for long, slender columns that fail primarily by elastic buckling before crushing. It assumes the material remains within the elastic limit and the column has a high slenderness ratio. Short columns fail mainly by crushing, and intermediate/medium columns are better analyzed using empirical formulas like Rankine’s formula. Therefore, the correct option is (a) long columns.
Which of the following is a positive drive?
A)
Crossed flat belt drive
B)
Crossed V-belt drive
C)
Rope drive
D)
Chain drive
A positive drive is one in which there is no slip between the driver and the driven member, so the velocity ratio remains exact. Chain drive is a positive drive because power is transmitted by engagement of chain links with sprocket teeth.
Why others are incorrect:
- Crossed flat belt drive: belt drives work by friction, so slip and creep can occur.
- Crossed V-belt drive: V-belts also transmit power by friction, so they are not positive drives.
- Rope drive: rope drives are also friction drives and may slip.
Therefore, the correct answer is Chain drive.
Zero axial thrust is experienced in
A)
helical gears
B)
bevel gears
C)
spiral gears
D)
herringbone gears
In helical gears, the inclined teeth produce an axial thrust along the shaft. Bevel and spiral gears also generate axial components of force. Herringbone gears consist of two opposite-hand helical gear sets placed side by side, so the axial thrust produced by one half is cancelled by the other half. Therefore, the net axial thrust is zero.
The number of instantaneous centres for a four bar chain is
A)
3
B)
4
C)
6
D)
12
For a mechanism with n links, the number of instantaneous centres is n(n−1)/2. A four-bar chain has 4 links, so the number of instantaneous centres is 4×3/2 = 6. Hence, the correct option is (c).