JNTU
JNTU B.Tech II ELEMENTS OF MECHANICAL ENGINEERING Previous Question Paper (April/May - 2023 - R13)
Note: i) Question paper consists of Part A, Part B. ii) Part A is compulsory, which carries 25 marks. In Part A, Answer all questions. iii) In Part B, Answer any one question from each unit. Each question carries 10 marks and may have a, b as sub questions.
Part A
Define modulus of elasticity.
Answer
Modulus of elasticity, also known as Young's modulus, is defined as the ratio of tensile or compressive stress to the corresponding tensile or compressive strain within the elastic limit of a material. It is a measure of the stiffness of a solid material and is expressed by the formula:
where E is the modulus of elasticity, σ is the stress, and ε is the strain. Its SI unit is Pascals (Pa) or N/m2.
Define thermal strains and stresses.
Answer
Thermal strain is the deformation produced in a material due to a change in its temperature. When a material is heated or cooled, it expands or contracts, respectively. If the material is free to expand or contract, no stress is induced, and the thermal strain is given by the formula:
where α is the coefficient of linear thermal expansion and ΔT is the change in temperature.
Thermal stress is the internal stress developed within a material when its natural thermal expansion or contraction is restricted or prevented by external constraints. If a material is prevented from expanding or contracting, the resulting stress is calculated as:
where E is the Young's modulus of the material. These stresses can lead to structural failure if not properly accounted for in engineering design.
Define shear force.
Answer
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Write a short note on cantilever beam with neat sketch.
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Define longitudinal stress.
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Write a short note on circumferential stress.
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Define indicated thermal efficiency.
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List out the difference between four stroke and 2 stroke engines.
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Define a gear train.
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Differentiate open belt and cross belt drives.
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Part B
Define E, K and N and derive relation between E and N.
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Derive the strain and stress for a vertical bar due to self-weight.
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A copper rod of 40 mm diameter is surrounded tightly by a cast iron tube of 80 mm external diameter; the ends being firmly fastened together. Calculate the sharing of load when subject to a compressive load of 30 kN. Also, calculate the decrease in length of the composite system if it is 2 m long. Take ECU = 75 GPa and ECI = 175 GPa.
Answer
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What are the assumptions made in simple theory of bending?
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Derive relation between bending moment and bending stress.
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A horizontal beam AD, 10 m long, carries a uniformly distributed load of 360 N/m run, together with a concentrated load of 900 N at the left-hand end A. The beam is supported at B, 1 m from A, and at C, which is the right-hand half of the beam, x m from D. Determine the value of x if the mid-point of the beam is a point of inflexion. Plot BM diagram.
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A circular disc of uniform thickness, rotating about its axis. Derive the expression for radial and circumferential stresses.
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A closed cylindrical drum 500mm in diameter and 2m long has a shell thickness of 12mm. If it carries a fluid under a pressure of 2 N/mm2, calculate the longitudinal and hoop stress in the drum wall and also determine the change in diameter, change in length and change in volume of the drum. Take E= 200 Gpa and 1/m=0.3.
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Differentiate petrol engine and diesel engine.
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A petrol engine uses per kWh 0.26 kg of fuel of calorific value 44000 kJ/kg. The mechanical efficiency is 78% and the compression is 5.6 to 1. Calculate: i) brake thermal efficiency ii) indicated thermal efficiency.
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The following data are known for a four cylinder four stroke petrol engine cylinder dimensions 11 cm bore, 13 cm stroke, engine speed 2250 rpm, break power 50 KW, friction power 15KW and fuel consumption rate 10.5 kg/hr, calorific value of fuel 50,000 kJ/kg, air inhalation rate 300 kg/h, ambient condition 150C, 1.03 bar. Estimate a) Break mean effective pressure b) Volumetric efficiency c) Break thermal efficiency and Mechanical efficiency.
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Write a short note on different types of gear trains.
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A pulley is driven by a flat belt running at a speed of 600 m/min. The coefficient of friction between the pulley and the belt is 0.3 and the angle of lap is 1600. If the maximum tension in the belt is 700 N, find the power transmitted by a belt.
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An open belt system is transmitting 10 KW power. Driving pulley is of diameter 200 mm and driven pulley is of diameter 480 mm. Center distance between the pulleys is 2 m. Maximum stress in belt is not to exceed 2.2 Mpa. Thickness of the belt is 8mm. Determine breadth and length of the belt. Assume density of belt material is 950 kg/m3, coefficient of friction between belt and pulley is 0.3. Driving pulley is rotating at 1000 rpm. Neglect bending stress in belt.
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