The Froude number Fr = V/√(gD) for channel flow determines the flow type. For Fr = 0.8, the flow is classified as:
Answer: B
Fr < 1 indicates subcritical (tranquil) flow, Fr = 1 is critical, and Fr > 1 is supercritical (rapid) flow. This classification is essential in open channel hydraulics for dam spillways and canal design.
Q.82Medium
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.83Medium
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.
Q.84Medium
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.85Medium
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).
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Q.86Medium
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.87Medium
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.88Medium
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.89Medium
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.91Medium
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.92Medium
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?
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.
Q.94Medium
A gear pair is designed with a contact ratio of 1.4. What does this indicate about the gear mesh?
Answer: B
A contact ratio of 1.4 means that on average 1.4 teeth are in mesh. Typically, one tooth carries the load while occasionally two teeth share the load briefly, ensuring smooth transmission.
Q.95Medium
A coupling is required for a motor-pump assembly where slight misalignment and vibration are expected. Which coupling type is MOST suitable?
Answer: B
Flexible couplings with elastomeric elements can accommodate angular, axial, and parallel misalignments while damping vibration, making them ideal for motor-pump assemblies with expected misalignment.
Q.96Medium
In the design of a flat belt drive, what is the primary criterion for determining the belt width?
Answer: A
Belt width in flat belt drives is primarily determined by the power transmission requirement and the belt speed. Higher power requires wider belts, while higher speeds may require adjustments.
Q.97Medium
In spring design, what is the primary effect of shot peening on the fatigue strength of a spring?
Answer: B
Shot peening creates compressive residual stresses at the surface, which significantly improve fatigue strength by preventing crack initiation and propagation from the surface.
Q.98Medium
A V-belt drive shows signs of slipping. Which of the following is NOT a likely cause?
Answer: C
Increasing pulley diameter would actually increase the belt length and tension, reducing slipping tendency. All other options reduce the friction coefficient or normal force, causing slipping.
Q.99Medium
In a brake design, which material property is MOST critical for brake pad selection?
Answer: B
Brake pads must maintain stable friction coefficient across varying temperatures and offer excellent wear resistance to provide consistent and safe braking performance throughout their service life.
Q.100Medium
In helical gear design, why is the helix angle typically limited to less than 45 degrees?
Answer: B
As helix angle increases, axial thrust component increases significantly. Limiting it to less than 45° keeps axial forces manageable and prevents excessive bearing loads and gear dimensions.
