Which of the following is the primary function of a key in mechanical design?
Answer: A
A key is a mechanical element that prevents relative rotational motion between a shaft and a hub or pulley by transmitting torque.
Q.2Easy
In gear design, what does the term 'Module' represent?
Answer: A
Module is defined as the ratio of pitch circle diameter to the number of teeth (m = D/N). It determines the size of the gear teeth.
Q.3Easy
Which bearing type is most suitable for high-speed applications with moderate loads?
Answer: B
Deep groove ball bearings are ideal for high-speed applications with moderate radial and axial loads due to their low friction and good precision.
Q.4Medium
The fatigue strength of a material is typically determined at how many cycles of stress reversal?
Answer: C
Fatigue strength is conventionally determined at 10^7 cycles for ferrous materials and 10^8 cycles for non-ferrous materials in standard fatigue testing.
Q.5Medium
A welded joint is subjected to a tensile load of 50 kN. If the weld has a size of 6 mm and length of 100 mm, what is the average shear stress in the weld?
Answer: A
Shear stress = Load/(Weld size × Length × 0.707) = 50,000/(6 × 100 × 0.707) ≈ 41.67 MPa. The factor 0.707 accounts for the throat area of the weld.
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Q.6Medium
Which of the following factors does NOT directly influence the selection of a coupling?
Answer: C
While all factors affect coupling design, the material of the shaft itself is not a direct selection criterion. Torque, speed, and misalignment are primary factors.
Q.7Medium
In screw thread design, what does the pitch angle represent?
Answer: A
The pitch angle (also called helix angle) is the angle made by the thread with the axis of the screw, calculated as tan(α) = pitch/(π × d).
Q.8Easy
Which type of fit is used when a permanent assembly is required with no relative motion?
Answer: B
Interference fit (or press fit) results in permanent assembly with no relative motion, as the hole size is smaller than the shaft size, creating an interference.
Q.9Medium
In a belt drive system, the belt tensions on the tight side and slack side are 1200 N and 400 N respectively. What is the power transmitted at 600 RPM with a pulley diameter of 200 mm?
Answer: B
Power = (T1 - T2) × π × D × N / 60,000 = (1200 - 400) × π × 0.2 × 60600,000 ≈ 5.03 kW
Q.10Medium
What is the primary purpose of using a stress concentration factor (Kt) in fatigue analysis?
Answer: A
The stress concentration factor accounts for stress amplification due to geometric features like fillets, holes, and shoulders that create local stress rises.
Q.11Medium
In rolling contact bearings, what does the 'L10 life' represent?
Answer: B
L10 life is the bearing life at which 90% of an identical group of bearings will complete without spalling, or conversely, 10% will have failed.
Q.12Medium
A hollow circular shaft has outer diameter 50 mm and inner diameter 30 mm. Calculate the polar moment of inertia.
Which surface finish is typically required for bearing bore surfaces?
Answer: B
Bearing bore surfaces typically require Ra 0.4 - 0.8 µm for proper fit and performance. Higher roughness can affect bearing life and accuracy.
Q.14Hard
In a riveted joint, if the shear strength of rivet material is 300 MPa and bearing strength is 400 MPa, which failure mode would occur first for a single rivet with 16 mm diameter?
Answer: A
Shear area = π/4 × 16² ≈ 201 mm². Shear failure load = 300 × 201 = 60,300 N. Bearing depends on thickness; shear typically governs for isolated rivet analysis.
Q.15Hard
What is the significance of the 'Hertzian stress' in rolling contact bearings?
Answer: B
Hertzian contact stress is the maximum compressive stress that occurs at the contact surface between rolling elements and raceways, critical for fatigue analysis.
Q.16Medium
In power screw design, what does the 'efficiency' of a screw represent?
Answer: A
Screw efficiency = (Load × pitch)/(2π × effort × radius). It represents the ratio of useful work output to the energy input, typically ranging from 25-90%.
Q.17Medium
A spur gear with 60 teeth and module 2 mm meshes with a pinion. If the center distance is 90 mm, how many teeth does the pinion have?
Which material property is MOST critical for designing a component subjected to cyclic loading?
Answer: B
For cyclic loading, fatigue strength and endurance limit are critical as they define the maximum stress that can be applied indefinitely without failure.
Q.19Easy
In a welded joint, which type of stress is primarily responsible for failure in a butt weld under tensile loading?
Answer: B
In butt welds under tensile loading, direct tensile stress perpendicular to the weld throat is the primary failure mode. The joint must be designed to resist this normal stress effectively.
Q.20Medium
A cast iron machine bed is subjected to fluctuating loads. Which material property is MOST important for its long-term reliability?
Answer: B
Cast iron's excellent damping capacity and reasonable fatigue strength make it ideal for machine beds subjected to fluctuating loads. Its ability to absorb vibration is a key advantage for structural components.
