Question 1

Belt drives: when is an open belt drive used?  Assume parallel shafts and standard flat/V-belt arrangements. Identify the shaft rotation condition that requires an open belt.  Choose the correct option.

Accepted Answer

Concept Open belt layouts are used when both pulleys must rotate in the same direction. A crossed belt reverses rotation (opposite directions). Why option (b) With parallel shafts and an open wrap, the belt does not cross; thus driving and driven pulleys rotate identically. Final Answer Parallel shafts rotating in the same direction

Question 2

Transmission shafts: identify what is included under the term ‘‘transmission shaft’’.  Select all that correctly fall under the category of transmission shafts used to transmit power. Choose the best option.

Accepted Answer

Concept Transmission shafts carry power between sources and machines. Examples include counter shafts (gearboxes), line shafts (shop power distribution), and overhead shafts (older factory layouts). All are within the definition. Final Answer All of these

Question 3

Bolts of uniform strength: verify the method involving drilling through the head.  Statement: To obtain a bolt of uniform strength, an axial hole is drilled through the head down to near the threaded portion so that the shank’s net area equals the t…

Accepted Answer

Concept A bolt of uniform strength is designed so the minimum cross-sectional area occurs uniformly along the length, avoiding stress concentration at the threaded root. One recognized method is to drill an axial hole in the head/shank so that the effective shank area ≈ thread root area. Alternative method Reducing the shank diameter to the root diameter is another common approach. Final Answer True

Question 4

Failure theories: identify Guest’s (maximum shear stress) theory statement.  Statement: Failure occurs when the maximum shear stress in a biaxial stress state reaches the shear stress at the elastic limit in a simple tension test.  Choose the correc…

Accepted Answer

Concept Guest's (Tresca) theory, also called the maximum shear stress theory, states that yielding begins when the maximum shear stress in a complex state equals that at yield in simple tension. The statement given is exactly this criterion. Contrast Distortion energy (von Mises) is a different criterion based on second deviatoric invariant. Final Answer True

Question 5

Boiler shell joints: purpose of circumferential joints. Statement: In boilers, circumferential joints are used to obtain the required length of a boiler by joining shell rings end-to-end. Choose the correct option (True/False).

Accepted Answer

Concept Boiler shell plates are assembled as rings. Circumferential joints join these rings end-to-end to build overall length. Longitudinal joints join plate edges along the length to form the shell diameter. Final Answer True

Question 6

Gears: factor governing surface endurance (pitting) strength.  Identify the material property that most directly influences the surface endurance limit in contact (Hertzian) stress for gears.  Choose the correct option.

Accepted Answer

Concept Surface endurance (pitting resistance) under Hertzian contact correlates strongly with surface hardness. Brinell hardness number (or similar hardness scales) is used in gear contact stress formulas (e.g., via allowable contact stress). Why BHN Higher hardness generally raises the allowable contact stress and delay pitting compared to yield/toughness alone. Final Answer Brinell hardness number (BHN)

Question 7

Screw jack design: purpose of a separate load cup on the spindle head.  Select the main functional reason for making the load cup a separate piece from the spindle head in a screw jack.  Choose the correct option.

Accepted Answer

Concept A separate load cup (often with a swiveling/ball seating) allows the load platform to remain stationary in rotation while the screw turns. This prevents rotation of the load, reduces scuffing, and accommodates slight misalignment. Notes Capacity and effort are more influenced by screw geometry and friction; the separate cup primarily addresses rotation and alignment. Final Answer Prevent rotation of the load being lifted

Question 8

Classification of shafts in machine design  A crankshaft used in engines is to be classified by type (e.g., transmission shaft, line shaft, machine shaft). Choose the most appropriate classification.

Accepted Answer

Concept In machine design, shafts are broadly grouped as transmission shafts (line/counter shafts used to transmit power between machines) and machine shafts (integral parts of machines). A crankshaft is a built, shaped member inside an engine that converts reciprocating motion to rotary motion and carries cranks, pins, and webs—hence it is a machine shaft. Why other options are incorrect • Transmission, line, and counter shafts transmit power between machine elements but are not integral kinematic members like a crankshaft. Final Answer Machine shaft

Question 9

V-belt vs. flat-belt drives: identify the incorrect statement  Consider power transmission, center distance suitability, direction of running, and tension ratio. Select the statement that is wrong.

Accepted Answer

Given Four statements about V-belt vs. flat-belt characteristics. Concept/Approach • V-belts are preferred for short to moderate centre distances; flat belts suit larger centres. • V-groove wedging increases the effective friction and thus the permissible tension ratio compared to flat belts. • A V-belt can run in either direction; tight side may be on top or bottom depending on layout. Evaluation • Option B claims V-belts are used for large centre distances — this is false (flat belts are preferred there). • Option D is true: the tension ratio is higher due to wedging. • Option C is true for belt drives. • Option A (as worded) is not the standard design takeaway; due to wedging, V-belts typically transmit more power than a flat belt under otherwise similar constraints. However, among the choices, the clearly incorrect and commonly tested statement regarding application is B. Final Answer The V-belt drive is used with large centre distance.

Question 10

Ball bearings: purpose of the cage (retainer)  Identify the primary function served by the cage in a ball bearing. Choose the correct option.

Accepted Answer

Concept The cage (retainer) keeps the balls evenly spaced, preventing contact between adjacent rolling elements, guiding ball paths, and permitting uniform load distribution. It is not a seal (lubricant retention is by shields/seals) and does not exist to promote slip. Final Answer To maintain the balls at a fixed distance apart

Question 11

Involute gears: centre distance of a meshing pair  State the relationship that gives the centre distance between two meshing involute gears. Choose the correct expression.

Accepted Answer

Concept For standard involute gears in mesh, the geometric centre distance equals the sum of the operating pitch circle radii (equivalently, (d₁ + d₂)/2). Base, addendum, and dedendum circles do not determine the centre distance directly. Final Answer Sum of pitch circle radii (i.e., (d₁ + d₂)/2)

Question 12

Effect of heating on toughness (impact energy capacity)  When a metallic material is heated, how does its toughness generally change? Choose the correct trend.

Accepted Answer

Concept Toughness reflects the ability to absorb energy before fracture (area under the stress–strain curve). For most ductile metals, increasing temperature reduces brittleness and increases ductility, so impact energy and toughness rise with heating (within typical service ranges). Final Answer Increases

Question 13

Flange coupling: method of joining the two flanges  Identify how the mating flanges in a standard rigid flange coupling are secured together. Choose the correct option.

Accepted Answer

Concept Rigid flange couplings employ bolts and nuts through matching flange holes to clamp the two halves together while the keys transmit torque from shaft to hub. Final Answer Bolts and nuts

Question 14

Relative ductility comparison among common engineering metals  Which listed material exhibits the highest ductility (greatest uniform elongation before fracture)? Choose the correct option.

Accepted Answer

Concept Among the given choices, copper is notably ductile (high percent elongation and reduction of area). Mild steel and aluminium are ductile but generally lower than copper; zinc is comparatively less ductile and more prone to brittleness at room temperature. Final Answer Copper

Question 15

Riveted joints: Unwin's formula for rivet diameter vs. plate thickness  Let t (mm) be the plate thickness. According to Unwin's empirical relation, select the correct expression for rivet hole diameter d (mm). Choose the correct option.

Accepted Answer

Concept Unwin's empirical relation (metric) gives rivet diameter as a function of plate thickness t (mm): d = 6 √t (mm)for common boiler/structural riveting practice (with variants like d ≈ 1.2√t in inches). Why others are incorrect Options (a)–(d) are linear in t and do not match the established square-root relation used in design charts and handbooks. Final Answer d = 6 √t

Question 16

Examples of class-III (third-type) levers  Identify the device that operates as a third-type lever (effort between fulcrum and load). Choose the correct example.

Accepted Answer

Concept • Class-III (third-type) lever: effort lies between fulcrum and load (e.g., forearm, fishing rod, hand-pump handle). • Safety-valve lever (with weight) and tongs are commonly modeled as class-I arrangements (fulcrum between load and effort); punching press hand wheel is not a lever example. Final Answer Handle of a hand pump

Question 17

Torsion: solid vs. hollow shaft with identical length, weight, and material  Two shafts A (solid) and B (hollow) have the same length, weight, and material; both are under pure torsion. State the correct comparative statement about their torsional s…

Accepted Answer

Given • Same material ⇒ same allowable shear stress (τallow) and shear modulus G. • Same length and weight ⇒ for the hollow shaft, material is distributed farther from the center. Concept Torque capacity at a given τ scales with the polar section modulus Zp; torsional stiffness scales with the polar moment of inertia J: Tmax = τallow · Zp, θ = T L / (G J)For a given mass, moving material outward (hollowing) increases both J and Zp, hence higher torque capacity and lower twist. Result A hollow shaft of equal weight/length is stronger in torsion and has greater torsional rigidity than a solid shaft. Final Answer The hollow shaft is stronger and stiffer for the same weight

Question 18

Preferred numbers (Renard series): constant factor for the R10 series  In engineering standardization, the Renard R10 series uses a constant ratio between successive preferred numbers. What is the constant factor (common ratio) for the R10 series?

Accepted Answer

Concept The Renard R5/R10/R20 series are geometric progressions. For R10, the common ratio is the tenth root of 10. Step-by-step Common ratio, r = 10^(1/10)r ≈ 10^0.1 ≈ 1.2589 ≈ 1.26 Common pitfall Confusing R10 with R5 (ratio ≈ 1.58) or R20 (ratio ≈ 1.12). Final Answer 1.26

Question 19

Sleeve (muff) coupling: design idealization for torsion  When analyzing a sleeve/muff coupling for power transmission, the sleeve is modeled as which type of torsional member? Choose the best option.

Accepted Answer

Concept A sleeve (muff) coupling transmits torque through the sleeve that encloses the shaft ends. In torsion analysis, the sleeve is treated as a hollow shaft resisting shear. Reasoning T = (π/16)·τallow·(Do^4 − Di^4)/DoThis is the torsion relation for a hollow circular member (sleeve). Common pitfall Modeling as a thin/thick pressure cylinder is incorrect; there is no internal pressure action—only torsion. Final Answer Hollow shaft

Question 20

Flanged pipe joint: bolt circumferential pitch for a leak-proof joint  For a flanged pipe joint, what range of circumferential pitch (bolt spacing along the circle), in terms of the bolt-hole diameter d, helps ensure a leak-proof joint? Choose the c…

Accepted Answer

Guideline For leak integrity and uniform gasket compression, typical design practice keeps circumferential bolt pitch within a moderate range. Rule of thumb A leak-proof flanged joint generally uses circumferential pitch: 20d ≤ pitch ≤ 30d. Common pitfall Too large a pitch risks local gasket relaxation and leaks; too small a pitch is uneconomical and unnecessary. Final Answer Between 20d and 30d

Machine Design Questions