BT-203 Basic Mechanical Engineering - Jun 2022 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. 7 Marks
   aEnlist important mechanical properties of engineering materials. Define any three with suitable examples.
   How to answer

   • List key mechanical properties: strength, elasticity, plasticity, ductility, malleability, hardness, toughness, brittleness, fatigue, creep
   • Select any three (e.g., ductility, hardness, toughness)
   • Provide definitions for the selected three properties
   • Give suitable engineering material examples for each
2. 7 Marks
   bA plate, $0.025\text{ mm}$ distant from a fixed plate, moves at $60\text{ cm/s}$ and requires a force of $2\text{ N/unit area}$ i.e. $2\text{ N/m}^2$ to maintain this speed. Determine the fluid viscosity between the plates.
   How to answer

   • Convert units: $dy = 0.025\times 10^{-3}\text{ m}$, $du = 0.6\text{ m/s}$
   • State Newton's law of viscosity: $\tau = \mu (du/dy)$
   • Substitute values: $2 = \mu (0.6 / 0.025\times 10^{-3})$
   • Calculate dynamic viscosity $\mu = 8.33\times 10^{-5}\text{ N}\cdot\text{s/m}^2$ (or $\text{Pa}\cdot\text{s}$)
3. 7 Marks
   aExplain the experimental set up of tensile testing of steel. Also compare stress-strain diagrams of ductile and brittle materials.
   How to answer

   • Describe UTM components (crosshead, grips, load cell, extensometer)
   • Explain specimen preparation and test procedure for mild steel
   • Draw and compare stress-strain curves for ductile (distinct yield, necking) and brittle (no necking, direct rupture) materials
   • Highlight key differences in elastic/plastic behavior
4. 7 Marks
   bFind the young's modulus of a brass rod of diameter $25\text{ mm}$ and of length $250\text{ mm}$ which is subjected to a tensile load of $50\text{ kN}$ when the extension of the rod is equal to $0.3\text{ mm}$.
   How to answer

   • Calculate cross-sectional area: $A = \frac{\pi}{4}(25)^2 \approx 490.87\text{ mm}^2$
   • Use elongation formula: $\Delta L = \frac{P L}{A E}$
   • Substitute values: $E = \frac{50\times 10^3 \times 250}{490.87 \times 0.3}$
   • Calculate $E \approx 84.87\times 10^3\text{ N/mm}^2 = 84.87\text{ GPa}$
5. 7 Marks
   aWith a neat diagram explain the main parts of a drilling machine. Explain any two operations performed on a drilling machine.
   How to answer

   • Neat sketch of drilling machine (upright/bench drilling machine)
   • Label and explain main parts: base, column, table, spindle, drill head, feed mechanism
   • Explain any two operations in detail (e.g., reaming, boring, counterboring, countersinking, or tapping)
6. 7 Marks
   bIn a boiler test the following quantities were obtained ; mean temperature of the feed $20^\circ\text{C}$; mean boiler pressure $10\text{kgf/cm}^2$, mean steam dryness $0.9$, coal burnt/ hr $250\text{kg}$, water supplied to boiler per hour $2260\text{ kg}$. The mass of water in the boiler at the end of the test was less than that at the commencement by $240\text{ kg}$. Calculate: i) The actual evaporation per kg of coal and ii) The equivalent evaporation. [Take data as: - at $10\text{ kgf/cm}^2$; $h_{f1} = 181.3\text{ kcal/kg}$; $h_{fg} = 482\text{ kcal/kg}$]
   How to answer

   • Total steam generated per hour: $m_s = 2260 + 240 = 2500\text{ kg/hr}$
   • Actual evaporation per kg of coal: $m_a = \frac{2500}{250} = 10\text{ kg steam/kg coal}$
   • Enthalpy of wet steam: $h = h_{f1} + x \cdot h_{fg} = 181.3 + 0.9 \times 482 = 615.1\text{ kcal/kg}$
   • Enthalpy of feed water: $h_{f0} = 20\text{ kcal/kg}$ (since $c_p = 1\text{ kcal/kg}\cdot^\circ\text{C}$)
   • Calculate equivalent evaporation: $m_e = \frac{m_a (h - h_{f0})}{539.0} = \frac{10 \times (615.1 - 20)}{539.0} \approx 11.04\text{ kg of steam/kg coal}$
7. 7 Marks
   aWhat are the various methods used for temperature measurement? Explain any one of them.
   How to answer

   • Enlist different temperature measurement instruments/methods: liquid-in-glass thermometer, bimetallic thermometer, thermocouples, resistance temperature detectors (RTDs), thermistors, radiation/optical pyrometers
   • Select one method (e.g., thermocouple based on Seebeck effect)
   • Explain working principle, construction, and operation of the chosen device
   • Draw schematic diagram and state practical applications
8. 7 Marks
   bDefine welding. Classify welding processes. Explain arc welding process.
   How to answer

   • Define welding as a permanent joining process using heat and/or pressure with or without filler material
   • Classify welding processes: fusion welding (gas, arc, thermit) and solid-state welding (resistance, friction, forge)
   • Explain arc welding: principle of electric arc formation between electrode and workpiece
   • Draw circuit/setup diagram of shielded metal arc welding (SMAW) and mention its applications
9. 7 Marks
   aWhat is the reciprocating pump? Explain its working with a neat sketch.
   How to answer

   • Define reciprocating pump as a positive displacement pump where a piston/plunger moves back and forth inside a cylinder
   • Draw neat labeled schematic showing cylinder, piston, piston rod, crank, connecting rod, suction pipe with valve, delivery pipe with valve
   • Explain suction stroke: crank rotation creates partial vacuum, suction valve opens, liquid enters cylinder
   • Explain delivery stroke: piston moves forward, pressure rises, delivery valve opens, liquid is forced out into delivery pipe
10. 7 Marks
    bDerive an expression for efficiency of Carnot cycle with neat sketches of PV and TS diagrams.
    How to answer

    • Draw P-V and T-s diagrams for Carnot cycle detailing the 4 reversible processes (1-2 isothermal expansion, 2-3 adiabatic expansion, 3-4 isothermal compression, 4-1 adiabatic compression)
    • Write heat supplied during isothermal expansion: $Q_1 = m R T_1 \ln(V_2/V_1)$
    • Write heat rejected during isothermal compression: $Q_2 = m R T_2 \ln(V_3/V_4)$
    • Use adiabatic relations to show $V_2/V_1 = V_3/V_4$
    • Derive thermal efficiency: $\eta = \frac{W}{Q_1} = \frac{Q_1 - Q_2}{Q_1} = 1 - \frac{T_2}{T_1}$
11. 7 Marks
    aState Pascal's law. Derive Bernoulli's equation. What are the assumptions made in Bernoulli's equation?
    How to answer

    • State Pascal's law: pressure at any point in a static fluid is equal in all directions
    • List assumptions for Bernoulli's equation: steady flow, incompressible fluid, inviscid/frictionless, flow along a streamline, irrotational
    • Derive Euler's equation of motion along a streamline: $\frac{dp}{\rho} + v\,dv + g\,dz = 0$
    • Integrate Euler's equation to obtain Bernoulli's equation: $\frac{p}{\rho g} + \frac{v^2}{2g} + z = \text{constant}$
12. 7 Marks
    bDiscuss, how the steam generators are classified. Give example of each classification.
    How to answer

    • Define steam generator / boiler
    • Classify based on content in tubes: Fire tube (Cochran, Lancashire) vs Water tube (Babcock and Wilcox)
    • Classify based on axis: Horizontal, Vertical, Inclined
    • Classify based on firing: Internally fired vs Externally fired
    • Classify based on pressure: High pressure (Benson, Velox) vs Low pressure (Cochran, Lancashire)
    • Classify based on circulation: Natural vs Forced circulation
13. 7 Marks
    aDefine thermodynamic system and explain open, close and isolated systems.
    How to answer

    • Define thermodynamic system: a specified region in space upon which study is focused
    • Define open system: both mass and energy cross the boundary (e.g., turbine, pump)
    • Define closed system: energy crosses the boundary but mass does not (e.g., piston-cylinder without valves)
    • Define isolated system: neither mass nor energy crosses boundary (e.g., universe, perfectly insulated thermos flask)
    • Provide summary comparison table and diagrams
14. 7 Marks
    bExplain the working of two stroke petrol engine with neat sketch.
    How to answer

    • Neat labeled sketch of two-stroke petrol engine showing cylinder, piston with deflector, spark plug, crankcase, inlet port, transfer port, exhaust port
    • Explain Upward stroke (compression and suction): compression of fuel-air mixture in cylinder while drawing fresh mixture into crankcase
    • Explain Downward stroke (power, exhaust, and transfer): combustion pushes piston down; exhaust port opens first, followed by transfer port for scavenging
    • Explain role of deflector piston in preventing direct loss of fresh charge
15. 14 Marks
    Write Short notes on (Any two) a) Casting defects b) Micrometre c) Dial gauge d) Different types of fluids
    How to answer

    • For Casting defects: Describe major defects like blowholes, shrinkage cavity, cold shuts, misruns, and hot tears with causes and remedies
    • For Micrometre: Explain principle of screw and nut, parts (anvil, spindle, thimble, ratchet stop), least count calculation
    • For Dial gauge: Explain rack and pinion mechanism, dial graduations, plunger movement, application for checking runout/flatness
    • For Different types of fluids: Define and classify ideal fluid, real fluid, Newtonian fluid, non-Newtonian fluid, ideal plastic/Bingham plastic with shear stress vs velocity gradient graph