JNTU
JNTU B.Tech II ELEMENTS OF MECHANICAL ENGINEERING Previous Question Paper (March - 2022 - R13)
Answer any five questions. All questions carry equal marks.
Main
Distinguish between compound bar and composite bar.
Answer
A composite bar consists of two or more different materials rigidly fixed together such that they act as a single unit when subjected to an external load. The strain in each material is the same, and the total load is shared among the materials based on their individual cross-sectional areas and elastic moduli.
A compound bar refers to a system where bars of different materials are connected in series or parallel, but the term is often used interchangeably with composite bars in engineering mechanics. However, strictly speaking, a compound bar implies a structural assembly where individual members are connected to resist loads collectively, often involving different thermal expansion properties or varying cross-sections, whereas composite bars specifically emphasize the unified material behavior under axial loading.
The modulus of rigidity for a material is 0.51×105 N/mm2. A 10 mm diameter rod of the material was subjected to an axial pull of 10 kN and the change in diameter was observed to be 3×10-3 mm. Calculate Poisson’s ratio and the modulus of elasticity.
Answer
Given: Modulus of rigidity (G) = 0.51 × 105 N/mm2, Diameter (d) = 10 mm, Axial load (P) = 10,000 N, Change in diameter (Δd) = 3 × 10-3 mm.
1. Calculate Stress (σ):
2. Calculate Lateral Strain (εl):
3. Calculate Poisson's ratio (μ):
Using the relationship between lateral strain and longitudinal strain (εl = -μ × εp), we first need the modulus of elasticity (E). Since E = 2G(1+μ) and εp = σ/E, we have εl = -μ(σ / (2G(1+μ))). Solving for μ:
Given the relationship between G, E, and μ, we find μ ≈ 0.25.
4. Calculate Modulus of Elasticity (E):
A compound bar consists of a steel cylinder which surrounds a copper cylinder. Both cylinders have a cross sectional area of 0.005 m2. The compressive stress in the copper cylinder is 100 MN/m2. Esteel = 200 GPa, Ecopper = 95 GPa, αsteel = 12 × 10-6, αcopper = 17 × 10-6. Calculate the (a) compressive force acting on the compound bar, and (b) stress in the steel cylinder. If the temperature of the loaded compound bar is now raised by 300°C, calculate the (c) stress in the steel and copper cylinders.
Answer
Sign in to view the complete answer paper.
Deduce the relation between shear force and intensity of loading.
Answer
Sign in to view the complete answer paper.
A simply supported beam of span 9 m is loaded with a varying load of intensity zero at the left hand side and 3 kN/m at the right side. Draw the S.F and B.M diagrams.
Answer
Sign in to view the complete answer paper.
Derive the bending equation from fundamentals:
Answer
Sign in to view the complete answer paper.
A 120 mm × 50 mm I-section is subjected to a shearing force of 10 kN. Calculate the shear stress at the neutral axis and at the top of the web. Given I = 220×104 mm4. Area = 9.4×102 mm2, web thickness = 3.5 mm and flange thickness = 5.5 mm.
Answer
Sign in to view the complete answer paper.
A cylindrical pipe has a 250 mm inner diameter and 500 mm outer diameter. It is subjected to an internal pressure of 35 MPa. Show the radial and circumferential stress variation across the wall thickness of the pipe.
Answer
Sign in to view the complete answer paper.
A thin cylinder of 300 mm internal diameter, 3 m long and made from 3 mm thick metal, has its ends blanked off. Working from first principles, except that you may use the equations derived above, find the change in capacity of this cylinder when an internal fluid pressure of 20 bar is applied. E = 200 GN/m2; μ = 0.3.
Answer
Sign in to view the complete answer paper.
Derive the equations for the circumferential and longitudinal stresses in a thin cylindrical shell.
Answer
Sign in to view the complete answer paper.
A thick cylinder of 100 mm internal radius and 150 mm external radius is subjected to internal pressure of 60 MN/m2 and external pressure of 30 MN/m2. Determine the hoop and radial stresses at the inside and outside of the cylinder together with the longitudinal stress if the cylinder is assumed to have closed ends.
Answer
Sign in to view the complete answer paper.
Discuss in detail the differences between Compression Ignition and Spark Ignition engines.
Answer
Sign in to view the complete answer paper.
A four stroke, compression ignition engine with four cylinders develops an indicated power of 125 kW and delivers a brake power of 100 kW. Calculate the (i) frictional power, and (ii) mechanical efficiency of the engine.
Answer
Sign in to view the complete answer paper.
Show that the centrifugal tension is independent of the tight and slack side tensions and depends only on the velocity of the belt over the pulley.
Answer
Sign in to view the complete answer paper.
The smaller pulley of a flat belt drive has a radius of 220 mm and rotates at 480 rpm. The angle of lap is 155°. The initial tension in the belt is 1.8 kN and the coefficient of friction between the belt and the pulley is 0.3. Determine the power transmitted by the belt.
Answer
Sign in to view the complete answer paper.