BT-203 Basic Mechanical Engineering - Jun 2025 Question Paper

Under each question, How to answer lists the points an answer should cover, outlined by CampusPrep from the syllabus. Check the details against your textbook.

1. 8 Marks
   aClassify engineering materials. What do you mean by alloys? Write some applications of alloys.
   How to answer

   • Classification chart of engineering materials: metals, polymers, ceramics, composites
   • Definition of alloy (solid solution or compound of two or more elements with metallic properties)
   • Key reasons for alloying (enhance strength, corrosion resistance, hardness)
   • Important engineering applications (steel in construction, brass/bronze in marine/bushings, duralumin in aerospace)
2. 6 Marks
   bDefine the following Mechanical properties:

   1. i)Toughness
   2. ii)Brittleness
   3. iii)Tensile strength
   4. iv)Ductility
   How to answer

   • Toughness: Ability of a material to absorb energy and plastically deform before fracturing
   • Brittleness: Tendency to fracture with little to no prior plastic deformation when stressed
   • Tensile strength: Maximum tensile stress a material can withstand before breaking/necking
   • Ductility: Measure of a material's ability to undergo significant plastic deformation under tensile stress before rupture (e.g., drawing into wires)
3. 8 Marks
   aDescribe the construction and use of sine bar. How will you measure taper of a job with the help of a sine bar.
   How to answer

   • Construction: High-carbon chromium steel body, precision ground rollers of equal diameter at known distance $L$
   • Principle: Trigonometric relation $\sin\theta = h / L$
   • Setup for taper measurement: Place job on surface plate, sine bar over job or job on sine bar, slip gauges beneath one roller
   • Procedure: Use dial test indicator across the taper surface until reading is parallel/zero, calculate angle using formula
4. 6 Marks
   bDescribe the procedure of a tensile test. Explain the stress-strain curve for a ductile material.
   How to answer

   • Tensile test procedure on UTM: Specimen preparation, gripping, applying tensile load gradually until fracture
   • Draw engineering stress-strain curve for mild steel
   • Label salient points: Proportional limit, elastic limit, upper & lower yield points, UTS, and fracture/rupture point
   • Brief explanation of elastic region, plastic region, necking phenomenon
5. 8 Marks
   aWith a neat diagram explain the main parts of a drilling machine? Explain any two operations performed on drilling machine.
   How to answer

   • Neat sketch of drilling machine (upright or radial type)
   • Key parts: Base, column, work table, spindle head, spindle, feed mechanism, drill chuck
   • Explanation of any two operations: Drilling, reaming, boring, counterboring, countersinking, or tapping
6. 6 Marks
   bWhat is the basic principle of turbine? Classify various types of turbines according to type of energy, direction of flow head and specific speed.
   How to answer

   • Basic working principle: Conversion of hydraulic energy (kinetic + pressure) into mechanical energy via rotating runner blades
   • Classification based on action of water: Impulse (Pelton wheel) vs Reaction (Francis, Kaplan)
   • Classification based on direction of flow: Tangential, radial, axial, mixed flow
   • Classification based on head: High head (>250 m), medium head (60-250 m), low head (<60 m)
   • Classification based on specific speed: Low, medium, high specific speed
7. 7 Marks
   aExplain working of a thermocouple and radiation pyrometer with neat sketches.
   How to answer

   • Thermocouple: Working based on Seebeck effect (emf generated across hot and cold junctions of dissimilar metals), circuit diagram
   • Radiation pyrometer: Non-contact measurement based on thermal radiation emitted by a hot body ($E = \sigma T^4$)
   • Optical/radiation pyrometer diagram and functional description of lens, target, receiving element/filament
8. 7 Marks
   bThe water is flowing through a pipe having diameters $25\text{ cm}$ and $10\text{ cm}$ at section 1 and 2 respectively. The rate of flow of water through the pipe is $30\text{ lit/sec}$. Section 1 is $10\text{ m}$ above the ground and section 2 is $2\text{ m}$ above the ground. If pressure at section 1 is $40\text{ N/cm}^2$, find the pressure at section 2.
   How to answer

   • Convert units: $d_1 = 0.25\text{ m}$, $d_2 = 0.10\text{ m}$, $Q = 0.03\text{ m}^3/\text{s}$, $P_1 = 40 \times 10^4\text{ N/m}^2$, $\rho = 1000\text{ kg/m}^3$
   • Calculate areas $A_1 = \frac{\pi}{4}(0.25)^2$, $A_2 = \frac{\pi}{4}(0.10)^2$
   • Calculate velocities $V_1 = Q/A_1 \approx 0.611\text{ m/s}$, $V_2 = Q/A_2 \approx 3.82\text{ m/s}$
   • Apply Bernoulli's equation: $\frac{P_1}{\rho g} + \frac{V_1^2}{2g} + z_1 = \frac{P_2}{\rho g} + \frac{V_2^2}{2g} + z_2$
   • Substitute values and solve for $P_2$ in $\text{N/m}^2$ or $\text{N/cm}^2$
9. 7 Marks
   aDescribe the construction and working principle of the pelton wheel?
   How to answer

   • Introduction: High-head, low-discharge tangential flow impulse turbine
   • Main components: Nozzle with spear mechanism, runner with hemispherical double-cup buckets, casing, breaking jet
   • Working principle: High velocity water jet strikes splitter of the bucket, momentum change drives runner rotation
   • Schematic sketch showing nozzle, runner, and bucket cross-section
10. 7 Marks
    bWhat is constant volume process? Derive expressions for the work done, change in internal energy heat transfer and change in enthalpy.
    How to answer

    • Definition of constant volume (isochoric) process ($V_1 = V_2$)
    • Work done: $W = \int P dV = 0$ since $dV = 0$
    • Change in internal energy: $\Delta U = m c_v (T_2 - T_1)$
    • Heat transfer from first law: $Q = \Delta U + W = \Delta U = m c_v (T_2 - T_1)$
    • Change in enthalpy: $\Delta H = m c_p (T_2 - T_1)$
11. 7 Marks
    aDefine internal energy and prove that energy is a property of a system?
    How to answer

    • Definition of internal energy as microscopic kinetic and potential energy of molecules
    • Consider two different cycles between states 1 and 2: Cycle 1 via Path A & Path B, Cycle 2 via Path A & Path C
    • Apply $\oint (\delta Q - \delta W) = 0$ to both cycles
    • Show $(\delta Q - \delta W)_B = (\delta Q - \delta W)_C$, proving $dE$ depends only on end states and not on path
    • Conclusion: Energy is a point function and thus a property of the system
12. 7 Marks
    bState the first law of thermodynamics for a closed system undergoing a cyclic process and non-cyclic process.
    How to answer

    • First law for cyclic process: The cyclic integral of heat transfer is equal to the cyclic integral of work transfer, $\oint \delta Q = \oint \delta W$
    • First law for non-cyclic process: Heat added to a system equals increase in internal energy plus work done by the system, $Q = \Delta U + W$ (or $\delta Q = dU + \delta W$)
    • Sign conventions and physical significance of energy conservation
13. 8 Marks
    aExplain the structure and working of two stroke diesel engine with a neat sketch?
    How to answer

    • Structure: Cylinder, piston with deflector crown, crankcase, inlet port, transfer port, exhaust port, fuel injector
    • Working: Upward stroke (compression of air in cylinder, suction of air into crankcase) and fuel injection near TDC
    • Downward stroke (power/expansion, exhaust blowdown, scavenging through transfer port)
    • Neat schematic sketch showing ports and piston movement
14. 6 Marks
    bWith the help of a neat sketch describe the construction and working of a steam engine?
    How to answer

    • Construction: Cylinder, piston, piston rod, crosshead, connecting rod, crank, flywheel, steam chest, D-slide valve, eccentric
    • Working principle: High-pressure steam enters through D-slide valve alternately to either side of double-acting cylinder, pushing piston
    • Conversion of reciprocating motion into rotary motion through slider-crank mechanism
    • Neat labeled sketch of double-acting steam engine
15. 14 Marks
    Write short note on any three

    1. i)Newton's law of viscosity
    2. ii)Zeroth law of thermodynamics
    3. iii)Micrometer
    4. iv)Centrifugal compressor
    How to answer

    • Newton's law of viscosity: Shear stress is proportional to velocity gradient, $\tau = \mu \frac{du}{dy}$
    • Zeroth law of thermodynamics: If two bodies are in thermal equilibrium with a third body, they are in thermal equilibrium with each other; basis of temperature measurement
    • Micrometer: Precision measuring instrument using screw and nut principle, parts (anvil, spindle, sleeve, thimble, ratchet), least count calculation
    • Centrifugal compressor: Dynamic compressor using rotating impeller to add kinetic energy followed by diffuser to convert kinetic energy into pressure rise