BT-203 Basic Mechanical Engineering - Nov 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
   aExplain the methods to measure the hardness of materials.
   How to answer

   • Definition of hardness
   • Brinell Hardness Test: indenter, load application, BHN formula
   • Rockwell Hardness Test: minor and major loads, depth of penetration, scales
   • Vickers Hardness Test: diamond pyramid indenter, diagonal measurement
2. 7 Marks
   bA flat plate of area $1.5 \times 10^6\text{ mm}^2$ is pulled with a speed of $0.4\text{ m/s}$ relative to another plate located at a distance of $0.15\text{ mm}$ from it. Find the force and power required to maintain this speed, if the fluid separating them is having viscosity as $1\text{ poise}$. [$1\text{ poise} = 0.1\text{ N s/m}^2$]
   How to answer

   • Convert units: $A = 1.5\text{ m}^2$, $dy = 0.15 \times 10^{-3}\text{ m}$, $\mu = 0.1\text{ N s/m}^2$
   • Calculate shear stress $\tau = \mu \frac{du}{dy} = 0.1 \times \frac{0.4}{0.15 \times 10^{-3}} = 266.67\text{ N/m}^2$
   • Calculate force: $F = \tau \cdot A = 266.67 \times 1.5 = 400\text{ N}$
   • Calculate power: $P = F \cdot u = 400 \times 0.4 = 160\text{ W}$
3. 7 Marks
   aClassify engineering materials. What do you mean by alloys? Write some applications of alloys.
   How to answer

   • Broad classification of engineering materials: metals (ferrous, non-ferrous), polymers, ceramics, composites
   • Definition of alloys: homogeneous mixture of two or more metals or a metal and non-metal
   • Reasons for alloying: improve strength, corrosion resistance, hardness
   • Key engineering applications of alloys (e.g., steel, brass, bronze, duralumin)
4. 7 Marks
   bA rod $200\text{ cm}$ long and of diameter $3.0\text{ cm}$ is subjected to an axial pull of $30\text{ kN}$. If the Young's modulus of the material of the road is $2 \times 10^5\text{ N/mm}^2$, determine: i) Stress ii) Strain iii) Elongation of the road
   How to answer

   • Convert units: $L = 2000\text{ mm}$, $d = 30\text{ mm}$, $P = 30000\text{ N}$
   • Area $A = \frac{\pi}{4} (30)^2 \approx 706.86\text{ mm}^2$
   • i) Stress $\sigma = \frac{P}{A} = \frac{30000}{706.86} \approx 42.44\text{ N/mm}^2$
   • ii) Strain $\epsilon = \frac{\sigma}{E} = \frac{42.44}{2 \times 10^5} \approx 2.122 \times 10^{-4}$
   • iii) Elongation $\delta L = \epsilon \cdot L = 2.122 \times 10^{-4} \times 2000 \approx 0.424\text{ mm}$
5. 7 Marks
   aWith a neat diagram explain the main parts of a lathe machine. Explain any two operations performed on a lathe machine.
   How to answer

   • Neat labeled diagram of a lathe machine
   • Main parts: Bed, Headstock, Tailstock, Carriage (saddle, apron, cross-slide, compound rest, tool post), Feed mechanism, Lead screw
   • Explanation of any two operations (e.g., Turning, Facing, Knurling, Thread cutting)
6. 7 Marks
   bDuring a trial operation of a boiler $1630\text{ kg}$ of coal were consumed in $24\text{ hrs.}$ and $13000\text{ kg}$ of water evaporated. The mean steam pressure was $7\text{ kgf/cm}^2$ and condition dry saturated. The fuel contained $3\text{ percent}$ moisture and $4\text{ percent}$ ash and had a calorific value of $7200\text{ kcal/kg}$. The feed water temperature was $35^\circ\text{C}$. Determine i) The boiler efficiency ii) The equivalent evaporation per kg of dry coal iii) The equivalent evaporation per kg of combustibles.
   How to answer

   • Find steam enthalpy $h = h_g$ at $7\text{ kgf/cm}^2$ from steam tables and feed enthalpy $h_{f1}$ at $35^\circ\text{C}$
   • Calculate actual evaporation per kg of coal: $m_a = \frac{13000}{1630} = 7.975\text{ kg/kg of coal}$
   • i) Boiler efficiency: $\eta_{boiler} = \frac{m_a (h - h_{f1})}{C} \times 100\%$
   • ii) Equivalent evaporation per kg of dry coal: $m_{e(dry)} = \frac{m_e}{1 - 0.03}$
   • iii) Equivalent evaporation per kg of combustibles: $m_{e(comb)} = \frac{m_e}{1 - 0.03 - 0.04}$
7. 7 Marks
   aExplain the working of a manometer for pressure measurement. Also relate absolute pressure, gauge pressure and vacuum pressure.
   How to answer

   • Principle of U-tube manometer using hydrostatic balance: $P = \rho g h$
   • Working explanation with a schematic
   • Relationship: $P_{abs} = P_{atm} + P_{gauge}$
   • Relationship: $P_{abs} = P_{atm} - P_{vacuum}$
   • Graphical representation comparing absolute, gauge, vacuum, and atmospheric pressure
8. 7 Marks
   bExplain the measurement process using vernier calliper with neat sketch.
   How to answer

   • Labeled sketch of a Vernier Calliper showing main scale, vernier scale, jaws, and depth gauge
   • Definition and derivation of Least Count (LC = 1 MSD - 1 VSD)
   • Step-by-step procedure for taking a reading: Total Reading = Main Scale Reading + (Vernier Scale Reading × LC)
   • Accounting for zero errors (positive and negative)
9. 7 Marks
   aDefine Viscosity. What is the importance of viscosity while selecting fluids in various engineering applications?
   How to answer

   • Definition of viscosity: internal resistance to flow / shear deformation
   • Newton's law of viscosity and mathematical expression $\tau = \mu \frac{du}{dy}$
   • Importance in lubrication: prevents metal-to-metal contact, film thickness
   • Importance in hydraulic systems, pumps, pipelines, and fuel atomization
10. 7 Marks
    bDiscuss briefly the differences between externally fired and internally fired steam generators. Also discuss the application of each type of steam generators.
    How to answer

    • Definition and distinction based on furnace location relative to boiler shell
    • Comparison table: furnace inside shell vs outside shell, examples (Lancashire/Cochran vs Babcock & Wilcox)
    • Pressure and steam capacity differences
    • Specific industrial applications for internally fired (low pressure, small capacity, process steam) and externally fired (high pressure power plants)
11. 7 Marks
    aExplain working principle of hydraulic turbines (Pelton wheel) with neat sketch.
    How to answer

    • Classification: tangential flow impulse turbine suitable for high head and low discharge
    • Neat labeled sketch of Pelton wheel showing nozzle, spear, runner, hemispherical/elliptical buckets, and casing
    • Working mechanism: conversion of pressure energy to kinetic energy via nozzle, impulse force exerted on buckets by jet deflection
12. 7 Marks
    bDerive an expression for efficiency of Otto cycle with neat sketches of PV and TS diagrams.
    How to answer

    • Draw neat P-V and T-S diagrams of the ideal Otto cycle with four processes: 1-2 isentropic compression, 2-3 constant volume heat addition, 3-4 isentropic expansion, 4-1 constant volume heat rejection
    • Formulate heat supplied $Q_{in} = m c_v (T_3 - T_2)$ and heat rejected $Q_{out} = m c_v (T_4 - T_1)$
    • Write thermal efficiency $\eta = 1 - \frac{Q_{out}}{Q_{in}} = 1 - \frac{T_4 - T_1}{T_3 - T_2}$
    • Use isentropic relations $T_2/T_1 = (V_1/V_2)^{\gamma-1} = r^{\gamma-1}$ and $T_3/T_4 = r^{\gamma-1}$ to derive $\eta = 1 - \frac{1}{r^{\gamma-1}}$
13. 7 Marks
    aState the Zeroth Law of thermodynamics. How is mercury in thermometer able to find the temperature of a body using the Zeroth law of thermodynamics?
    How to answer

    • Statement of Zeroth Law: If two bodies A and B are each in thermal equilibrium with a third body C, they are in thermal equilibrium with each other
    • Concept of temperature as an indicator of thermal equilibrium
    • Application to thermometer: Body A is the object, Body B is calibrated scale / thermometer casing, Body C is mercury
    • Explanation of thermal equilibrium established between body and mercury leading to reproducible expansion
14. 7 Marks
    bExplain the working of four stroke diesel engine with neat sketch.
    How to answer

    • Neat sketches depicting the four strokes: Suction, Compression, Power/Expansion, Exhaust
    • Suction stroke: intake of air only
    • Compression stroke: high compression ratio, temperature reaches fuel auto-ignition point
    • Power stroke: diesel injected and ignited, high-pressure expansion
    • Exhaust stroke: burnt gases expelled via exhaust valve
15. 14 Marks
    Write Short notes on (Any two): a) Welding defects b) Dial gauge c) Sine bar d) Thermodynamic properties
    How to answer

    • a) Welding defects: porosity, undercut, slag inclusion, lack of penetration/fusion, cracks, causes and remedies
    • b) Dial gauge: working principle (rack and pinion mechanism), components, applications in checking flatness, parallelism, runout
    • c) Sine bar: principle based on trigonometry $\sin\theta = \frac{h}{L}$, construction, use with slip gauges for precise angle measurement
    • d) Thermodynamic properties: definition, intensive vs extensive properties with examples (pressure, temperature vs volume, mass)