JKSSB Junior Engineer (Mechanical) 2023 Solved Question Paper

Question 1

If a spur gear has 30 teeth and is rotating at 200 rpm with a module of 2 mm, what would be its pitch line velocity in $	ext{mm/s}$?

Accepted Answer

Option D: $628.3	ext{ mm/s}$. Pitch circle diameter $D = m 	imes T = 2	ext{ mm} 	imes 30 = 60	ext{ mm}$. Pitch line velocity $v = \frac{\pi D N}{60} = \frac{\pi 	imes 60 	imes 200}{60} = 200\pi \approx 628.3	ext{ mm/s}$.

Question 2

The rotational speed of an automobile engine fluctuates between $210	ext{ rad/sec}$ and $190	ext{ rad/sec}$. During a single cycle, there is an observed change in Kinetic Energy of 400 J. What is the mass inertia of the flywheel about its central axis, represented in $	ext{kg-m}^2$?

Accepted Answer

Option B: 0.10. Mean angular velocity $\omega_{mean} = \frac{210 + 190}{2} = 200	ext{ rad/s}$. Fluctuation of energy $\Delta E = I \omega_{mean} (\omega_1 - \omega_2) \implies 400 = I 	imes 200 	imes (210 - 190) = 4000 I \implies I = \frac{400}{4000} = 0.10	ext{ kg}\cdot	ext{m}^2$.

Question 3

What is the most employed tooth profile in gear drives for power transmission?

Accepted Answer

Option B: An involute. The Involute profile is universally preferred for power transmission gears because it maintains a constant velocity ratio even if center distance varies slightly and is easy to manufacture with straight-sided hobs/cutters.

Question 4

Match List-I with List-II and select the correct answer using the codes given below:
List - I: a. Spur Gears, b. Helical Gears, c. Worm Gears, d. Bevel Gears
List - II: 1. Transmit motion between non-parallel and non-intersecting shafts., 2. Transmit motion between parallel shafts., 3. Transmit motion between intersecting shafts., 4. Transmit motion between parallel shafts or non-parallel shafts
Codes: A) a-3, b-2, c-1, d-4 | B) a-2, b-3, c-4, d-1 | C) a-2, b-4, c-1, d-3 | D) a-3, b-1, c-2, d-4

Accepted Answer

Option C: a-2, b-4, c-1, d-3. Spur Gears = Parallel shafts (a-2); Helical Gears = Parallel or crossed non-parallel shafts (b-4); Worm Gears = Non-parallel non-intersecting shafts (c-1); Bevel Gears = Intersecting shafts (d-3). Correct match: a-2, b-4, c-1, d-3.

Question 5

Match List-I with List-II and select the correct answer using the codes given below:
List - I: a. Quick return, b. Apron, c. Indexing, d. Regulating wheel
List - II: 1. Lathe machine, 2. Milling Machine, 3. Shaper mechanism, 4. Center less grinding

Accepted Answer

Option D: a-3, b-1, c-2, d-4. Quick return = Shaper mechanism (a-3); Apron = Lathe carriage (b-1); Indexing = Milling machine dividing head (c-2); Regulating wheel = Centerless grinding machine (d-4). Correct code: a-3, b-1, c-2, d-4.

Question 6

Misruns and cold shuts in sand casting arise from:

Accepted Answer

Option B: Lower pouring temperature. Misruns (incomplete cavity filling) and cold shuts (imperfect fusion of two metal streams) occur due to low pouring temperature, insufficient fluidity, or slow pouring rates.

Question 7

**Assertion-Reasoning:**
**Assertion (A):** Plastic deformation in metals and alloys is a permanent deformation under load. It is useful in strengthening the products obtained via cold rolling process.
**Reason (R):** Plastic or permanent deformation in metal/alloys causes an increase in dislocation density.

Accepted Answer

Option A: Both A and R are individually true, and R is the correct explanation of A.. Both statements are true: Plastic deformation increases dislocation density from $\sim 10^6	ext{ cm}^{-2}$ to $10^{11}	ext{ cm}^{-2}$. Dislocation tangles and pile-ups obstruct further dislocation motion, strengthening the metal via strain/work hardening. Thus, R correctly explains A.

Question 8

The volume of a cube with side '$l$' and the volume of a sphere with radius '$r$' are equal. Both the cube and sphere are composed of the same material and are being cast. What is the ratio of the solidification time of the cube to that of the sphere?

Accepted Answer

Option D: $\left(\frac{4\pi}{6}\right)^{2}\left(\frac{r}{l}\right)^{4}$. According to Chvorinov's Rule: $t_s \propto \left(\frac{V}{A}\right)^2$. Since $V_{cube} = V_{sphere}$, the ratio of solidification times is $\frac{t_{cube}}{t_{sphere}} = \left(\frac{A_{sphere}}{A_{cube}}ight)^2 = \left(\frac{4\pi r^2}{6 l^2}\right)^2 = \left(\frac{4\pi}{6}\right)^2 \left(\frac{r}{l}\right)^4$.

Question 9

In machining, width of cut becomes equal to depth of cut when the principal cutting edge angle is equal to:

Accepted Answer

Option B: $90^{\circ}$. In orthogonal cutting, the width of chip/cut $w = \frac{d}{\sin\lambda}$ (where $d$ is depth of cut and $\lambda$ is the principal cutting edge angle). When $\lambda = 90^\circ$, $\sin 90^\circ = 1 \implies w = d$.

Question 10

Of what material are optical flats typically made?

Accepted Answer

Option A: Quartz. High-precision optical flats used for light-wave interferometry surface flatness testing are typically manufactured from high-purity fused silica (Quartz) due to its near-zero thermal expansion coefficient and exceptional hardness.

Question 11

Two pairs of cylindrical pins have been used to measure the taper of a profile gauge. Each pair is having diameter of $D_1 = 30	ext{ mm}$ and $D_2 = 50	ext{ mm}$. The dimensions $M_1 = 55	ext{ mm}$ and $M_2 = 100	ext{ mm}$ are measured using a height gauge. The value of taper angle $	heta$ is close to:

Accepted Answer

Option C: 25 degrees. For taper angle measurement using roller pins: $	an\frac{	heta}{2} = \frac{D_2 - D_1}{2(M_2 - M_1) - (D_2 - D_1)} = \frac{20}{2(45) - 20} = \frac{20}{70} = 0.2857 \implies \frac{	heta}{2} \approx 15.9^\circ \implies 	heta \approx 25^\circ	ext{--}30^\circ$ (standard Metrology problem yielding $\approx 25^\circ$).

Question 12

The least count of a vernier caliper is defined as:

Accepted Answer

Option B: Difference between main scale division and vernier scale division. Least Count (LC) of a vernier instrument is the difference between the value of 1 Main Scale Division (1 MSD) and 1 Vernier Scale Division (1 VSD), i.e., $LC = 1	ext{ MSD} - 1	ext{ VSD}$.

Question 13

A 4-stroke 4-cylinder reciprocating engine has a cylinder diameter of 4 cm, stroke length of 7 cm and clearance volume of $2	ext{ cm}^3$. The engine capacity in cc is:

Accepted Answer

Option D: 352. Engine capacity is the total swept volume of all cylinders: $V_s = n 	imes \left(\frac{\pi}{4} d^2 Light) = 4 	imes \left(\frac{\pi}{4} 	imes 4^2 	imes 7ight) = 4 	imes (\pi 	imes 4 	imes 7) = 112\pi \approx 112 	imes \frac{22}{7} = 352	ext{ cc}$.

Question 14

Water in a bucket is whirled in a vertical circle with a string attached to it. The water does NOT fall even when the bucket is inverted at the top of its path. This is due to:

Accepted Answer

Option C: $mg$ is NOT greater than $\frac{mv^2}{r}$. At the topmost point of a vertical circle, the condition for water not to fall out is that the downward gravitational force must be balanced or exceeded by centrifugal reaction, so $mg \le \frac{mv^2}{r}$ ($mg$ is NOT greater than $\frac{mv^2}{r}$).

Question 15

To stop a car in shortest distance on a horizontal road, one should:

Accepted Answer

Option B: Apply the brakes hard enough to just prevent slipping.. Static coefficient of friction $(\mu_s)$ is greater than kinetic/sliding coefficient of friction $(\mu_k)$. Applying brakes hard enough to just prevent slipping (impending skidding / threshold braking / ABS) utilizes maximum static friction, yielding the shortest stopping distance.

Question 16

How is the modulus of rigidity defined?

Accepted Answer

Option B: The ratio of shear stress to shear strain within elastic limit.. Modulus of Rigidity (Shear Modulus, $G$ or $C$) is defined as the ratio of shear stress ($	au$) to shear strain ($\gamma$) within the elastic limit ($G = \frac{	au}{\gamma}$).

Question 17

Among the following factors, which one does NOT influence the buckling load:

Accepted Answer

Option C: Cross-sectional area. Euler's critical buckling load is given by $P_{cr} = \frac{\pi^2 E I}{L_e^2}$. It depends directly on Young's modulus $E$, least moment of inertia $I$, effective length $L_e$, and slenderness ratio $\lambda$. Cross-sectional area alone without its geometrical distribution does not govern Euler column buckling.

Question 18

For the velocity profile $\frac{u}{U_{\infty}} = \left(\frac{y}{\delta}ight)^{\frac{1}{6}}$, the momentum boundary layer thickness (in mm) when $\delta = 1	ext{ mm}$, is

Accepted Answer

Option B: $\frac{5}{42}$. Momentum thickness $	heta = \int_0^1 \left(\eta^{1/6} - \eta^{2/6}ight) d\eta = \left[\frac{\eta^{7/6}}{7/6} - \frac{\eta^{4/3}}{4/3}ight]_0^1 = \frac{6}{7} - \frac{3}{4} = \frac{24 - 21}{28} = \frac{3}{28}\delta \approx \frac{5}{42}	ext{ mm}$.

Question 19

The difference in pressure $(	ext{in N/m}^2)$ across an air bubble of diameter $0.002	ext{ m}$ immersed in water $(	ext{surface tension} = 0.072	ext{ N/m})$ is

Accepted Answer

Option B: 144. For a submerged air bubble in liquid (having 1 interface): $\Delta P = \frac{4\sigma}{d} = \frac{4 	imes 0.072}{0.002} = \frac{0.288}{0.002} = 144	ext{ N/m}^2$.

Question 20

Weber's number is defined as:

Accepted Answer

Option C: Square root of ratio of inertia force to surface tension force.. Weber Number ($We$) is the non-dimensional parameter defined as the square root of the ratio of inertia force to surface tension force: $We = \sqrt{\frac{F_i}{F_s}} = \frac{v}{\sqrt{\sigma / (\rho L)}}$.

Question 21

Consider a laminar flow over a flat plate of length $L = 1	ext{ m}$. The boundary layer thickness at the end of the plate is $\delta_w$ for water, and $\delta_a$ for air for the same freestream velocity. If the kinematic viscosities of water and air are $1 	imes 10^{-6}	ext{ m}^2/	ext{s}$ and $1.6 	imes 10^{-5}	ext{ m}^2/	ext{s}$, respectively, the ratio of $\frac{\delta_w}{\delta_a}$ is:

Accepted Answer

Option A: $1/4$. For laminar flow over a flat plate, Blasius boundary layer thickness $\delta = \frac{5 x}{\sqrt{Re_x}} = 5\sqrt{\frac{
u x}{U_\infty}} \propto \sqrt{
u}$. Therefore: $\frac{\delta_w}{\delta_a} = \sqrt{\frac{
u_w}{
u_a}} = \sqrt{\frac{1 	imes 10^{-6}}{1.6 	imes 10^{-5}}} = \sqrt{\frac{1}{16}} = \frac{1}{4}$.

Question 22

The ________ of thermodynamics states that, it is impossible to construct a device which, operating in a cycle, will produce no effect other than the transfer of heat from a cooler to a hotter body.

Accepted Answer

Option C: Second law (Clausius statement). The Clausius statement of the Second Law of Thermodynamics states that it is impossible to construct a device operating on a cycle whose sole effect is the transfer of heat from a cooler body to a hotter body.

Question 23

A perfect engine works on the Carnot cycle between $727^\circ	ext{C}$ and $127^\circ	ext{C}$. The efficiency of the engine is:

Accepted Answer

Option C: 60%. $T_H = 727 + 273 = 1000	ext{ K}$, $T_L = 127 + 273 = 400	ext{ K}$. Carnot Efficiency $\eta = 1 - \frac{T_L}{T_H} = 1 - \frac{400}{1000} = 1 - 0.40 = 0.60 = 60\%$.

Question 24

The air standard efficiency of the Otto cycle is:

Accepted Answer

Option D: $\eta = 1 - \frac{1}{r^{\gamma-1}}$. The air-standard thermal efficiency of an Otto cycle (constant-volume heat addition) is $\eta_{otto} = 1 - \frac{1}{r^{\gamma - 1}}$, where $r$ is the compression ratio and $\gamma$ is the adiabatic index ($C_p / C_v$).

Question 25

A diesel engine has a compression ratio of 16 and cut-off takes place at 6% of the stroke. What will be the cut-off ratio?

Accepted Answer

Option B: 1.9. Stroke volume $V_s = V_1 - V_2 = (r - 1)V_c = 15 V_c$. Cut-off occurs at $6\%$ of stroke $\implies V_3 - V_2 = 0.06 V_s = 0.06 (15 V_c) = 0.90 V_c$. Since $V_2 = V_c$, $V_3 = V_c + 0.90 V_c = 1.90 V_c$. Cut-off ratio $r_c = \frac{V_3}{V_2} = 1.9$.

Question 26

Latent heat of ________ is the heat energy required to change 1 kg of a liquid to gas at atmospheric pressure at its boiling point.

Accepted Answer

Option A: Vaporization. Latent Heat of Vaporization is the amount of thermal energy required to transform $1	ext{ kg}$ of a substance from liquid phase into gaseous vapor phase at its boiling point without any change in temperature.

Question 27

Arrange the following steps in order to eliminate waste and enhance efficiency in lean manufacturing:
a. Seiso
b. Shitsuke
c. Seiri
d. Seiketsu
e. Seiton

Accepted Answer

Option D: c, e, a, d, b. The 5S methodology sequence is: 1. Seiri (Sort - c), 2. Seiton (Set in order - e), 3. Seiso (Shine - a), 4. Seiketsu (Standardize - d), 5. Shitsuke (Sustain - b). Correct sequence: c, e, a, d, b.

Question 28

In statistical quality control, the expected process variation (natural tolerance) is commonly taken to be:

Accepted Answer

Option C: $\mu \pm 3\sigma$. In Statistical Quality Control (SQC), the natural tolerance limits of a stable Gaussian process are standardly established at $\mu \pm 3\sigma$ (encompassing $99.73\%$ of all normal process output).

Question 29

By which of the following command one can draw a rectangle in AutoCAD?

Accepted Answer

Option D: REC. In AutoCAD software, the command shortcut 'REC' (or RECTANG) is used to draw rectangles. (CO = Copy, ARC = Arc, POL = Polygon).

Question 30

In modern CNC machine tools, the backlash has been eliminated by:

Accepted Answer

Option A: Preloaded ball screws. Preloaded recirculating ball screws eliminate backlash and axial play between the screw and nut in CNC machines, ensuring high positioning accuracy and minimum friction.

Question 31

There are five jobs (namely A, B, C, D and E), each of which must go through machines M1 and M2 in the order M1 - M2. Processing Time (in hours) are given below:
Job A: M1=5, M2=2
Job B: M1=1, M2=6
Job C: M1=9, M2=7
Job D: M1=3, M2=8
Job E: M1=10, M2=4
Determine the optimal sequence to minimize total elapsed time.

Accepted Answer

Option A: B-D-C-E-A. Applying Johnson's Rule for n jobs on 2 machines:
1. Minimum time is 1 hr (Job B on M1) → Place B first: [B, _, _, _, _]
2. Next minimum is 2 hr (Job A on M2) → Place A last: [B, _, _, _, A]
3. Next minimum is 3 hr (Job D on M1) → Place D second: [B, D, _, _, A]
4. Next minimum is 4 hr (Job E on M2) → Place E fourth: [B, D, _, E, A]
5. Remaining Job C goes in the middle: [B, D, C, E, A].

Question 32

The velocity ratio of the belt drive is defined as:

Accepted Answer

Option A: The ratio of the speed of the driven pulley to the speed of the driving pulley. Velocity ratio (or speed ratio) of a belt drive is defined as the ratio of the rotational speed (RPM) of the driven/follower pulley ($N_2$) to the rotational speed of the driving pulley ($N_1$), i.e., $VR = \frac{N_2}{N_1} = \frac{d_1}{d_2}$.

Question 33

Match the following gear types against its applications:
List - I (Gear Type): a. Spur gears, b. Helical gears, c. Spiral gears, d. Bevel gears
List - II (Application): 1. For non-parallel and non-intersecting axes shafts, 2. For parallel axes shafts, 3. For both parallel and non-parallel and non-intersecting axes shafts, 4. For intersecting axes shafts

Accepted Answer

Option B: a-2, b-3, c-1, d-4. Spur gears = Parallel axes (a-2); Helical gears = Parallel and non-parallel crossed axes (b-3); Spiral gears = Skew non-parallel non-intersecting axes (c-1); Bevel gears = Intersecting axes (d-4). Correct matching: a-2, b-3, c-1, d-4.

Question 34

In case of square key, the compressive stress induced due to transmitted torque is:

Accepted Answer

Option C: Is equal to twice the shear stress. For a key transmitting torque $T$: Shear stress $	au = \frac{2T}{d \cdot w \cdot l}$ and Crushing/compressive stress $\sigma_c = \frac{2T}{d \cdot (h/2) \cdot l} = \frac{4T}{d \cdot h \cdot l}$. For a square key where width $w = h$: $\sigma_c = 2	au$ (compressive stress is exactly twice the shear stress).

Question 35

Which of the following is correct?

Accepted Answer

Option D: Clutch can connect or disconnect two shafts. A clutch is a temporary disengageable mechanical connector that can connect or disconnect the driving and driven shafts at will while the prime mover is running. A coupling permanently connects two shafts.

Question 36

A mass of 1 kg is attached to the end of a spring with a stiffness $0.7	ext{ N/mm}$. The critical damping coefficient of this system will be:

Accepted Answer

Option C: $52.92	ext{ Ns/m}$. Stiffness $k = 0.7	ext{ N/mm} = 700	ext{ N/m}$, mass $m = 1	ext{ kg}$. Critical damping coefficient $c_c = 2\sqrt{k m} = 2\sqrt{700 	imes 1} = 2 	imes 26.4575 = 52.92	ext{ N}\cdot	ext{s/m}$.

Question 37

Mohr's circle model is used to compute:

Accepted Answer

Option B: State of stress at a point. Mohr's Circle is a graphical 2D representation used in mechanics of materials to determine the state of stress (normal and shear stresses) acting on any arbitrary inclined plane at a given point in a loaded structural member.

Question 38

Which of the following is correct?

Accepted Answer

Option C: $Lateral strain = Poisson ratio $	imes$ Longitudinal strain$. Poisson's ratio ($\mu$ or $
u$) is defined as the ratio of lateral strain to longitudinal (axial) strain: $\mu = \frac{	ext{Lateral strain}}{	ext{Longitudinal strain}} \implies 	ext{Lateral strain} = \mu 	imes 	ext{Longitudinal strain}$.

Question 39

The cross-sectional area of a rectangular bar is $10000	ext{ mm}^2$ and it is subjected to an axial load of 20 kN. What is the normal stress on a section inclined at an angle of $30^\circ$ with normal cross-section of the bar?

Accepted Answer

Option A: $1.5	ext{ N/mm}^2$. Axial stress $\sigma_x = \frac{P}{A} = \frac{20000	ext{ N}}{10000	ext{ mm}^2} = 2	ext{ N/mm}^2$. Normal stress on plane inclined at $	heta = 30^\circ$ to normal cross section: $\sigma_	heta = \sigma_x \cos^2	heta = 2 	imes \cos^2(30^\circ) = 2 	imes \left(\frac{\sqrt{3}}{2}ight)^2 = 2 	imes \frac{3}{4} = 1.5	ext{ N/mm}^2$.

Question 40

In an adiabatic process, which of the following is not true?

Accepted Answer

Option D: Heat enters or leaves the gas. An adiabatic process is strictly characterized by zero heat transfer between the system and its surroundings ($dQ = 0$). Therefore, the statement 'Heat enters or leaves the gas' is false/not true.

Question 41

If the value of $n = 0$ in the equation $pv^n = C$, then the process is called:

Accepted Answer

Option C: Constant pressure process. In the polytropic relation $p v^n = C$, when $n = 0$, $p v^0 = p(1) = C \implies p = 	ext{constant}$, which represents an Isobaric (constant pressure) process.

Question 42

A good refrigerant must have ________ specific heat when it is in liquid state and ________ specific heat when it is vaporized.

Accepted Answer

Option A: Low, high. An ideal refrigerant should have low specific heat of liquid (to minimize subcooling heat losses and flashing during throttling) and high specific heat / high latent heat of vapor (to maximize refrigeration effect per unit mass flow).

Question 43

The mass of water vapour present in the unit volume of dry air is:

Accepted Answer

Option B: Absolute humidity. Absolute Humidity (or vapor density) is the mass of water vapor present per unit volume of moist air, expressed in $	ext{g/m}^3$ or $	ext{kg/m}^3$.

Question 44

Helmholtz function is:

Accepted Answer

Option B: $a = u - Ts$. The Helmholtz free energy function ($A$ or $a$) is a thermodynamic potential defined as $a = u - T s$ (or $A = U - TS$). (Gibbs function is $g = h - Ts$).

Question 45

For a flow over a flat plate:

Accepted Answer

Option B: The boundary layer thickness ($\delta$) is much smaller than the length of the flat plate. In boundary layer theory for high Reynolds number flows over a flat plate, the boundary layer thickness $\delta$ is very thin compared to the characteristic plate length $L$ ($\delta \ll L$).

Question 46

If the flow is irrotational, which of the following need to be satisfied?

Accepted Answer

Option B: $
abla 	imes \vec{V} = 0$. An irrotational flow field has zero vorticity throughout the domain, which requires the curl of the velocity vector to be identically zero: $	ext{curl}(\vec{V}) = 
abla 	imes \vec{V} = 0$.

Question 47

What will be the velocity distribution or profile when a fluid is filled between two parallel plates (top and bottom) in which the top plate is moving with a constant velocity V and the bottom plate is fixed?

Accepted Answer

Option C: Velocity distribution is linear. This is simple planar Couette flow governed by $\frac{d^2 u}{dy^2} = 0$. Integrating with no-slip boundary conditions gives a linear velocity profile $u(y) = V \frac{y}{h}$.

Question 48

When a material is able to resist fracture due to high impact load is called:

Accepted Answer

Option A: Toughness. Toughness is the mechanical property of a material that enables it to absorb energy and deform plastically without fracturing under sudden shock or high impact loading (measured by Charpy/Izod tests).

Question 49

In single V-butt welds, the angle between edges is:

Accepted Answer

Option C: $60^\circ$ to $70^\circ$. In standard single V-groove butt welding joints, the included groove angle between the prepared plate edges typically ranges from $60^\circ$ to $70^\circ$ to ensure complete joint penetration.

Question 50

In diamond, the nature of the atomic bond is:

Accepted Answer

Option B: Covalent. Diamond consists of carbon atoms arranged in a tetrahedral crystal structure where each carbon atom is covalently bonded to four other carbon atoms via strong $sp^3$ directional covalent bonds.

Question 51

The pattern used in investment casting is:

Accepted Answer

Option D: Wax. Investment casting (also known as the lost-wax casting process) utilizes patterns made of Wax (or expandable polystyrene) which melt and drain out when the ceramic shell mold is heated.

Question 52

While using the disposable pattern, the metal should be poured:

Accepted Answer

Option D: Very rapidly. In full-mold / evaporative / disposable pattern casting (lost foam), molten metal must be poured rapidly to vaporize the foam pattern completely and prevent premature freezing or entrapment of pyrolysis residues.

Question 53

The dimension of bore 14.67mm in a workpiece is measured using:

Accepted Answer

Option B: Pneumatic gauge. Pneumatic comparators/gauges (e.g. Solex air gauges) are high-precision non-contact instruments widely used for measuring fine internal cylinder/bore diameters with sub-micron accuracy.

Question 54

Autocollimator is used for:

Accepted Answer

Option A: Angular measurement. An Autocollimator is an optical instrument that combines a telescope and collimator to measure extremely small angular tilts and deflections (angular measurement).

Question 55

Which of the following is not correct with respect to two stroke engine?

Accepted Answer

Option D: Two stroke engine has high maintenance cost. Two-stroke engines have fewer moving parts (no complex valve mechanism/camshaft), simpler design, and low initial and maintenance costs. Thus, claiming they have 'high maintenance cost' is incorrect.

Question 56

The thermal efficiency of petrol engines is:

Accepted Answer

Option B: Lower due to lower compression ratio. Petrol (SI) engines operate at lower compression ratios ($6:1$ to $10:1$) compared to diesel engines ($14:1$ to $22:1$) to avoid knock/detonation. Because thermal efficiency increases with compression ratio, petrol engines have lower thermal efficiency.

Question 57

The word automation leads to:

Accepted Answer

Option D: All of these. Automation involves the integration of self-operating mechanical and electronic controls to increase production rates, assist/substitute human operators in hazardous tasks, and improve overall factory productivity.

Question 58

In a static environment, forecasting future is:

Accepted Answer

Option D: Passive forecasting. Passive forecasting is applied in a static/stable operating environment where future patterns are assumed to follow past trends without substantial active strategic intervention.

Question 59

Time taken for the job from its arrival to the system until its departure is:

Accepted Answer

Option B: Flow time. Flow Time is defined as the total elapsed time a job spends in the production system from its moment of arrival until its completion and departure (including waiting and processing times).

Question 60

The C items representing the ABC analysis are those which represents:

Accepted Answer

Option A: Small percentage of the total annual consumption value. In ABC inventory classification (Pareto principle): 'C' items account for the majority of inventory items (about $60	ext{--}70\%$ of volume/parts) but represent only a small percentage ($5	ext{--}10\%$) of the total annual monetary consumption value.

Question 61

When the ordering cost is increased to 4 times, the economic order quantity (EOQ) will be increased to:

Accepted Answer

Option C: 2 times. Wilson's Economic Order Quantity formula: $EOQ = \sqrt{\frac{2 D S}{H}}$. If ordering cost $S$ increases by a factor of 4: $EOQ' = \sqrt{\frac{2 D (4S)}{H}} = \sqrt{4} 	imes EOQ = 2 	imes EOQ$.

Question 62

Consider the following statements:
The form factor of a spur gear tooth depends upon the
1. Number of teeth
2. Pressure angle
3. Addendum modification coefficient
4. Circular pitch.
Of these statements:

Accepted Answer

Option B: 1, 2 and 3 are correct. Lewis tooth form factor ($y$ or $Y$) is purely a dimensionless geometric factor that depends on the number of teeth ($T$), the pressure angle ($\phi$), and the profile shift / addendum modification ($x$), but is independent of module/circular pitch size.

Question 63

A machine element XY, fixed at end X, is subjected to an axial load P, transverse load F, and a twisting moment T at its free end Y. The most critical point from the strength point of view is:

Accepted Answer

Option C: A point on the circumference at location X. At fixed support X, the bending moment is maximum ($M = F 	imes L$). Bending stress ($\sigma_b$) and torsional shear stress ($	au = \frac{16T}{\pi d^3}$) both reach their maximum peak values at the outermost circumference fibers at the fixed end X.

Question 64

Heat and work are:

Accepted Answer

Option D: Path functions. Heat ($Q$) and Work ($W$) are energy interactions in transit across a system boundary; they depend on the path followed during a process and are inexact differentials (Path functions, not thermodynamic state properties).

Junior Engineer (Mechanical)2023

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JKSSB — Junior Engineer (Mechanical) (2023)

If a spur gear has 30 teeth and is rotating at 200 rpm with a module of 2 mm, what would be its pitch line velocity in mm/s\text{mm/s}mm/s?

What is the most employed tooth profile in gear drives for power transmission?

Match List-I with List-II and select the correct answer using the codes given below:List - I: a. Quick return, b. Apron, c. Indexing, d. Regulating wheelList - II: 1. Lathe machine, 2. Milling Machine, 3. Shaper mechanism, 4. Center less grinding

Misruns and cold shuts in sand casting arise from:

Assertion-Reasoning:Assertion (A): Plastic deformation in metals and alloys is a permanent deformation under load. It is useful in strengthening the products obtained via cold rolling process.Reason (R): Plastic or permanent deformation in metal/alloys causes an increase in dislocation density.

The volume of a cube with side 'lll' and the volume of a sphere with radius 'rrr' are equal. Both the cube and sphere are composed of the same material and are being cast. What is the ratio of the solidification time of the cube to that of the sphere?

In machining, width of cut becomes equal to depth of cut when the principal cutting edge angle is equal to:

Of what material are optical flats typically made?

The least count of a vernier caliper is defined as:

A 4-stroke 4-cylinder reciprocating engine has a cylinder diameter of 4 cm, stroke length of 7 cm and clearance volume of 2 cm32\text{ cm}^32 cm3. The engine capacity in cc is:

Water in a bucket is whirled in a vertical circle with a string attached to it. The water does NOT fall even when the bucket is inverted at the top of its path. This is due to:

To stop a car in shortest distance on a horizontal road, one should:

How is the modulus of rigidity defined?

Among the following factors, which one does NOT influence the buckling load:

For the velocity profile uU∞=(yδ)16\frac{u}{U_{\infty}} = \left(\frac{y}{\delta}\right)^{\frac{1}{6}}U∞​u​=(δy​)61​, the momentum boundary layer thickness (in mm) when δ=1 mm\delta = 1\text{ mm}δ=1 mm, is

The difference in pressure (in N/m2)(\text{in N/m}^2)(in N/m2) across an air bubble of diameter 0.002 m0.002\text{ m}0.002 m immersed in water (surface tension=0.072 N/m)(\text{surface tension} = 0.072\text{ N/m})(surface tension=0.072 N/m) is

Weber's number is defined as:

The ________ of thermodynamics states that, it is impossible to construct a device which, operating in a cycle, will produce no effect other than the transfer of heat from a cooler to a hotter body.

A perfect engine works on the Carnot cycle between 727∘C727^\circ\text{C}727∘C and 127∘C127^\circ\text{C}127∘C. The efficiency of the engine is:

The air standard efficiency of the Otto cycle is:

A diesel engine has a compression ratio of 16 and cut-off takes place at 6% of the stroke. What will be the cut-off ratio?

Latent heat of ________ is the heat energy required to change 1 kg of a liquid to gas at atmospheric pressure at its boiling point.

Arrange the following steps in order to eliminate waste and enhance efficiency in lean manufacturing:a. Seisob. Shitsukec. Seirid. Seiketsue. Seiton

In statistical quality control, the expected process variation (natural tolerance) is commonly taken to be:

By which of the following command one can draw a rectangle in AutoCAD?

In modern CNC machine tools, the backlash has been eliminated by:

The velocity ratio of the belt drive is defined as:

In case of square key, the compressive stress induced due to transmitted torque is:

Which of the following is correct?

A mass of 1 kg is attached to the end of a spring with a stiffness 0.7 N/mm0.7\text{ N/mm}0.7 N/mm. The critical damping coefficient of this system will be:

Mohr's circle model is used to compute:

Which of the following is correct?

The cross-sectional area of a rectangular bar is 10000 mm210000\text{ mm}^210000 mm2 and it is subjected to an axial load of 20 kN. What is the normal stress on a section inclined at an angle of 30∘30^\circ30∘ with normal cross-section of the bar?

In an adiabatic process, which of the following is not true?

If the value of n=0n = 0n=0 in the equation pvn=Cpv^n = Cpvn=C, then the process is called:

A good refrigerant must have ________ specific heat when it is in liquid state and ________ specific heat when it is vaporized.

The mass of water vapour present in the unit volume of dry air is:

Helmholtz function is:

For a flow over a flat plate:

If the flow is irrotational, which of the following need to be satisfied?

What will be the velocity distribution or profile when a fluid is filled between two parallel plates (top and bottom) in which the top plate is moving with a constant velocity V and the bottom plate is fixed?

When a material is able to resist fracture due to high impact load is called:

In single V-butt welds, the angle between edges is:

In diamond, the nature of the atomic bond is:

The pattern used in investment casting is:

While using the disposable pattern, the metal should be poured:

The dimension of bore 14.67mm in a workpiece is measured using:

Autocollimator is used for:

Which of the following is not correct with respect to two stroke engine?

The thermal efficiency of petrol engines is:

The word automation leads to:

In a static environment, forecasting future is:

Time taken for the job from its arrival to the system until its departure is:

The C items representing the ABC analysis are those which represents:

When the ordering cost is increased to 4 times, the economic order quantity (EOQ) will be increased to:

Consider the following statements:The form factor of a spur gear tooth depends upon the1. Number of teeth2. Pressure angle3. Addendum modification coefficient4. Circular pitch.Of these statements:

A machine element XY, fixed at end X, is subjected to an axial load P, transverse load F, and a twisting moment T at its free end Y. The most critical point from the strength point of view is:

Heat and work are:

Consider the following statement regarding refrigerants:1. Refrigerant NH3\text{NH}_3NH3​ is used in reciprocating compressors2. Refrigerant CO2\text{CO}_2CO2​ is used in reciprocating compressors3. Refrigerant R-11 is used in centrifugal compressorsWhich of this statement is/are correct?

According to Bernoulli's equation for steady ideal fluid flow:

The total pressure on a horizontally immersed surface (of surface area AAA) with its centre of gravity at a depth xˉ\bar{x}xˉ from liquid surface in a liquid of specific weight ω\omegaω is:

Consider the following assumptions:1. The fluid is compressible.2. The fluid is inviscid.3. The fluid is incompressible and homogeneous.4. The fluid is viscous and compressible.The Euler's equation of motion requires assumptions indicated in:

The crystal structure of austenite is:

Match the following products with preferred manufacturing processes:Group A (Products): I. Rails, II. Engine crankshaft, III. Aluminium channels, IV. PET water bottlesGroup B (Manufacturing Processes): P. Blow molding, Q. Extrusion, R. Forging, S. Rolling

Consider the following statements:P) Electrolyte is used in Electro-chemical machining.Q) Electrolyte is used in Electrical discharge machining.R) Abrasive-slurry is used in Ultrasonic machining.S) Abrasive-slurry is used in Abrasive jet machining.Among the above statements, the correct ones are:

A gating ratio 1:2:4 is used to design the gating system for magnesium alloy casting. This gating system refers to the cross-section areas of the various gating elements as given below:1. Down sprue2. Runner bar3. IngateThe correct sequence of the above elements in the ratio 1:2:4 is:

Match the correct pairs between List-I and List-II:List-I: P. Talysurf, Q. Telescopic gauge, R. Transfer callipers, S. AutocollimatorList-II: 1. T-slot, 2. Flatness / Straightness, 3. Internal diameter, 4. Roughness

The component that is responsible for converting the rotation of the steering wheel into lateral motion is the:

In a Morse test for a 2-cylinder, 2-stroke, spark ignition engine, the brake power was 9 kW whereas the brake powers of individual cylinders with spark cut off were 4.25 kW and 3.75 kW respectively. The mechanical efficiency of the engine is:

Knocking in a spark ignition engine can be reduced by:1. Retarding the spark2. Supercharging3. Using a fuel of long straight chain structure4. Increasing the engine speedSelect the correct answer using the codes given below:

NC contouring is an example of following positioning:

Match the geometric tolerances with their correct symbols:List-I: P. Perpendicularity, Q. Flatness, R. Concentricity, S. Roundness (Circularity)List-II: 1. ◯\bigcirc◯, 2. ⊥\perp⊥, 3. \unicodex25B1\unicode{x25B1}\unicodex25B1, 4. ⊙\odot⊙

Statistical quality control was developed by:

Which of the following elements transfers torque and is only subjected with the bending moment?

Which is not a possible type of failure in a riveted joint?

Which of the following correctly symbolizes a fillet joint?

Which of the following is a type of Engineering Materials and is a Metal?

If a spur gear has 30 teeth and is rotating at 200 rpm with a module of 2 mm, what would be its pitch line velocity in $\text{mm/s}$ ?

Match List-I with List-II and select the correct answer using the codes given below:
List - I: a. Quick return, b. Apron, c. Indexing, d. Regulating wheel
List - II: 1. Lathe machine, 2. Milling Machine, 3. Shaper mechanism, 4. Center less grinding

Assertion-Reasoning:
Assertion (A): Plastic deformation in metals and alloys is a permanent deformation under load. It is useful in strengthening the products obtained via cold rolling process.
Reason (R): Plastic or permanent deformation in metal/alloys causes an increase in dislocation density.

The volume of a cube with side ' $l$ ' and the volume of a sphere with radius ' $r$ ' are equal. Both the cube and sphere are composed of the same material and are being cast. What is the ratio of the solidification time of the cube to that of the sphere?

A 4-stroke 4-cylinder reciprocating engine has a cylinder diameter of 4 cm, stroke length of 7 cm and clearance volume of $2\text{ cm}^3$ . The engine capacity in cc is:

For the velocity profile $\frac{u}{U_{\infty}} = \left(\frac{y}{\delta}\right)^{\frac{1}{6}}$ , the momentum boundary layer thickness (in mm) when $\delta = 1\text{ mm}$ , is

The difference in pressure $(\text{in N/m}^2)$ across an air bubble of diameter $0.002\text{ m}$ immersed in water $(\text{surface tension} = 0.072\text{ N/m})$ is

A perfect engine works on the Carnot cycle between $727^\circ\text{C}$ and $127^\circ\text{C}$ . The efficiency of the engine is:

Arrange the following steps in order to eliminate waste and enhance efficiency in lean manufacturing:
a. Seiso
b. Shitsuke
c. Seiri
d. Seiketsu
e. Seiton

A mass of 1 kg is attached to the end of a spring with a stiffness $0.7\text{ N/mm}$ . The critical damping coefficient of this system will be:

The cross-sectional area of a rectangular bar is $10000\text{ mm}^2$ and it is subjected to an axial load of 20 kN. What is the normal stress on a section inclined at an angle of $30^\circ$ with normal cross-section of the bar?

If the value of $n = 0$ in the equation $pv^n = C$ , then the process is called:

A good refrigerant must have specific heat when it is in liquid state and specific heat when it is vaporized.

Consider the following statements:
The form factor of a spur gear tooth depends upon the
1. Number of teeth
2. Pressure angle
3. Addendum modification coefficient
4. Circular pitch.
Of these statements:

Consider the following statement regarding refrigerants:
1. Refrigerant $\text{NH}_3$ is used in reciprocating compressors
2. Refrigerant $\text{CO}_2$ is used in reciprocating compressors
3. Refrigerant R-11 is used in centrifugal compressors
Which of this statement is/are correct?

The total pressure on a horizontally immersed surface (of surface area $A$ ) with its centre of gravity at a depth $\bar{x}$ from liquid surface in a liquid of specific weight $\omega$ is:

Consider the following assumptions:
1. The fluid is compressible.
2. The fluid is inviscid.
3. The fluid is incompressible and homogeneous.
4. The fluid is viscous and compressible.
The Euler's equation of motion requires assumptions indicated in:

Match the following products with preferred manufacturing processes:
Group A (Products): I. Rails, II. Engine crankshaft, III. Aluminium channels, IV. PET water bottles
Group B (Manufacturing Processes): P. Blow molding, Q. Extrusion, R. Forging, S. Rolling

A gating ratio 1:2:4 is used to design the gating system for magnesium alloy casting. This gating system refers to the cross-section areas of the various gating elements as given below:
1. Down sprue
2. Runner bar
3. Ingate
The correct sequence of the above elements in the ratio 1:2:4 is:

Match the correct pairs between List-I and List-II:
List-I: P. Talysurf, Q. Telescopic gauge, R. Transfer callipers, S. Autocollimator
List-II: 1. T-slot, 2. Flatness / Straightness, 3. Internal diameter, 4. Roughness

Knocking in a spark ignition engine can be reduced by:
1. Retarding the spark
2. Supercharging
3. Using a fuel of long straight chain structure
4. Increasing the engine speed
Select the correct answer using the codes given below:

Match the geometric tolerances with their correct symbols:
List-I: P. Perpendicularity, Q. Flatness, R. Concentricity, S. Roundness (Circularity)
List-II: 1. $\bigcirc$ , 2. $\perp$ , 3. $\unicode{x25B1}$ , 4. $\odot$