BT-203 Basic Mechanical Engineering - Jun 2023 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
   aExplain the Stress-Strain Diagram for ductile materials with neat sketch?
   How to answer

   • Sketch the stress-strain curve for a ductile material (mild steel) showing salient points.
   • Label proportional limit, elastic limit, upper and lower yield points, ultimate tensile strength point, and fracture/breaking point.
   • Explain elastic region and Hooke's law validity.
   • Explain yielding and plastic deformation region.
   • Explain necking and final fracture behavior.
2. 6 Marks
   bDefine the following: i) Young modulus ii) Elastic limit iii) Ultimate point
   How to answer

   • Define Young's modulus ($E = \sigma / \epsilon$) within proportional limit along with SI units (N/m² or Pa).
   • Define elastic limit as maximum stress up to which material regains its original shape upon unloading.
   • Define ultimate point (ultimate tensile strength) as the maximum nominal stress the material can sustain before necking/failure.
3. 8 Marks
   aExplain the effect of any 8 (eight) alloying element in alloy steel with details.
   How to answer

   • List 8 common alloying elements: Chromium (Cr), Nickel (Ni), Molybdenum (Mo), Tungsten (W), Vanadium (V), Manganese (Mn), Silicon (Si), Cobalt (Co) or Titanium (Ti).
   • Detail the specific effect of each on steel properties such as hardness, tensile strength, corrosion resistance, wear resistance, toughness, and hardenability.
4. 6 Marks
   bExplain feed mechanism used in a drilling machine.
   How to answer

   • Define feed in drilling (axial advancement of the drill per revolution).
   • Explain hand/manual feed mechanism (hand lever, pinion, and rack on the spindle sleeve).
   • Explain automatic/power feed mechanism (gear train driving the worm and worm gear connected to the pinion shaft).
   • Provide a schematic diagram of the mechanism.
5. 8 Marks
   aExplain the process of Pitot tube for velocity measurement of a Fluid with neat sketch.
   How to answer

   • Principle of Pitot tube: conversion of kinetic energy into pressure energy at the stagnation point.
   • Draw a neat schematic of a Pitot tube placed in fluid flow indicating static head and stagnation head.
   • Apply Bernoulli's equation between free stream and stagnation point to derive $v = C_v \sqrt{2gh}$.
   • Explain calculation of velocity head $h$ and measurement procedure.
6. 6 Marks
   bExplain the method of using Slip Gauge with the neat sketch.
   How to answer

   • Introduction to slip gauges (precision gauge blocks for standard linear measurement).
   • Detailed explanation of the 'wringing' phenomenon and step-by-step process of wringing two slip gauges together (cleaning, cross-positioning, rotating into alignment).
   • Draw neat sketches illustrating the wringing process.
   • Mention precautions in handling and temperature stability.
7. 8 Marks
   aThe dynamic viscosity of lubricating oil used between shaft and sleeve is 10 poise. The diameter of the shaft, which rotates at 200 rpm, is 0.5 m. The sleeve length is 100 mm. Calculate the power lost if the thickness of oil film is 2 mm?
   How to answer

   • Convert given units to SI: $\mu = 1\text{ N}\cdot\text{s}/\text{m}^2$, $D = 0.5\text{ m}$, $L = 0.1\text{ m}$, $t = 0.002\text{ m}$, $N = 200\text{ rpm}$.
   • Calculate surface velocity: $u = \pi D N / 60 = \pi \times 0.5 \times 200 / 60 = 5.236\text{ m/s}$.
   • Calculate shear stress: $\tau = \mu (u / t) = 1 \times (5.236 / 0.002) = 2618\text{ N/m}^2$.
   • Calculate shear force: $F = \tau \times (\pi D L) = 2618 \times (\pi \times 0.5 \times 0.1) = 41.12\text{ N}$.
   • Calculate power lost: $P = F \times u = 41.12 \times 5.236 \approx 215.3\text{ W}$.
8. 6 Marks
   bWhat is a draft tube? Why is it used in a reaction turbine? Describe with a neat sketch?
   How to answer

   • Define draft tube as an expanding conduit connecting runner exit to the tailrace.
   • Explain functions/purposes: recovering kinetic energy leaving the runner as pressure head, and allowing the turbine to be set above tailrace level without losing net head.
   • Provide a neat sketch showing runner outlet, draft tube, and tailrace.
   • Mention types of draft tubes (conical, simple elbow, moody spreading).
9. 8 Marks
   aExplain the working and construction of Pelton wheel turbine with neat sketch.
   How to answer

   • Classification: tangential flow, high head, low discharge impulse turbine.
   • Key construction parts: nozzle with spear mechanism, runner with hemispherical double-ellipsoidal buckets with splitter, casing, braking jet.
   • Working principle: High velocity water jet impinges on bucket splitters, changes momentum, produces torque.
   • Neat labeled sketch showing nozzle, spear, runner, and buckets.
10. 6 Marks
    bProve that work and heat are the path function.
    How to answer

    • Define point function vs. path function.
    • Draw a $p$-$V$ diagram showing a system changing from state 1 to state 2 via two different paths, A and B.
    • Show that the area under curve A is different from the area under curve B ($\int_A p\,dV \neq \int_B p\,dV$), proving work $W$ is a path function.
    • Using the First Law of Thermodynamics ($Q = \Delta U + W$), since $\Delta U$ is a point function and $W$ depends on path, $Q$ must also depend on the path, thus heat is a path function.
11. 8 Marks
    aExplain the working of Cochran boiler and fusible plug with neat sketches.
    How to answer

    • Describe Cochran boiler: vertical, multi-tubular, fire-tube boiler with hemispherical crown.
    • Explain working of Cochran boiler (combustion in firebox, hot gases passing through horizontal smoke tubes to chimney).
    • Draw neat sketch of Cochran boiler labeling grate, combustion chamber, flue tubes, and mountings.
    • Explain fusible plug: safety mounting fitted over crown plate; fuses when water level falls below critical limit to extinguish fire.
    • Draw sectional sketch of fusible plug showing bronze body, hexagonal nut, and fusible metal alloy.
12. 6 Marks
    bDerive an expression for the first law of thermodynamics applied to a closed system. Define the internal energy of a system.
    How to answer

    • State First Law for a cycle: $\oint \delta Q = \oint \delta W$.
    • Consider two cycles consisting of processes (1-A-2-B-1) and (1-A-2-C-1) to show $(\delta Q - \delta W)$ is identical for any path between states 1 and 2.
    • Establish that $(\delta Q - \delta W) = dE$ (or $dU$ when neglecting kinetic and potential changes), leading to $\delta Q = dU + \delta W$.
    • Define internal energy ($U$) as the microscopic energy stored in molecular motion, configuration, and intermolecular bonds.
13. 8 Marks
    aExplain the structure and working of four-stroke diesel engine with a neat sketch?
    How to answer

    • Describe key components: cylinder, piston, connecting rod, crankshaft, inlet valve, exhaust valve, and fuel injector.
    • Explain the four strokes in detail: Suction stroke (only air inducted), Compression stroke (high compression ratio heating the air), Power stroke (fuel injected, auto-ignition, expansion), Exhaust stroke (burnt gases expelled).
    • Provide neat sketches depicting piston motion and valve positions during the four strokes.
14. 6 Marks
    bExplain the working principle of the centrifugal compressor.
    How to answer

    • Describe basic working principle: air enters axially through eye of impeller and is turned radially outwards.
    • Explain action of impeller: mechanical energy increases kinetic energy and static pressure of air.
    • Explain action of diffuser and volute casing: converts high kinetic energy into static pressure energy.
    • Provide schematic sketch showing impeller, diffuser vanes, and casing.
15. 14 Marks
    Write Short note on any two: a) Thermodynamic system, properties and state. b) Working principle of steam Engine c) Casting and Patterns d) Impact testing of materials
    How to answer

    • For (a): Define closed/open/isolated system; intensive vs extensive properties; state and equilibrium.
    • For (b): Explain double-acting reciprocating steam engine cycle, cylinder, D-slide valve mechanism, and expansion of steam.
    • For (c): Define metal casting process; define pattern as replica of casting; list types of patterns and pattern allowances (shrinkage, draft, machining).
    • For (d): Explain objective of impact testing (measuring toughness/brittleness); brief description of Izod and Charpy pendulum impact tests.