Shafts, Keys & Couplings in Machine Design Multiple Choice Questions
1. Which of the following act on shafts?
A. Torsional moment
B. Bending Moment
C. Both torsional and bending
D. None of the mentioned
Answer: C
Explanation: Shaft is subjected to torsional moment as well as bending moment.
2. When the shaft is subjected to pure bending moment, the bending stress is given by?
A. None of the listed
B. 32M/πdᵌ
C. 16M/πdᵌ
D. 8M/πdᵌ
Answer: B
Explanation: Stress =My/I where y=d/2 and I=πd⁴/64.
3. When the shaft is subjected to pure torsional moment, the torsional stress is given by?
A. None of the listed
B. 32M/πdᵌ
C. 16M/πdᵌ
D. 8M/πdᵌ
Answer: C
Explanation: Stress=Mr/J where r=d/2 and J=πd⁴/64
4. Calculate the shaft diameter on rigidity basis if torsional moment is 196000N-mm, length of shaft is 1000mm. Permissible angle of twist per meter is 0.5’ and take G=79300N/mm².
A. None of the listed
B. 41.2mm
C. 35.8mm
D. 38.8mm
Answer: B
Explanation: d⁴=584Ml/Gθ.
5. If yielding strength=400N/mm², the find the permissible shear stress according to ASME standards.
A. 72 N/mm²
B. 76 N/mm²
C. 268 N/mm²
D. 422 N/mm²
Answer: A
Explanation: 0.18×400.
6. The stiffness of solid shaft is more than the stiffness of hollow shaft with same weight.
A. True
B. False
Answer: B
Explanation: Hollow shaft is more stiff.
7.The strength of hollow shaft is more than the strength of solid shaft of same weight.
A. True
B. False
Answer: A
Explanation: Outer fibers are more effective in resisting the applied moments. In hollow shafts material is removed and spread on a larger radius.
8. Solid shaft is costlier than hollow shaft of same weight.
A. True
B. False
Answer: B
Explanation: Hollow shaft cost is more as material is to be selectively emplaced.
9. Solid shafts are used in epicyclic gearboxes.
A. True
B. False
Answer: B
Explanation: In epicyclic gears, one shaft rotates inside other and hence hollow shafts are used.
10. Flexible shafts have _______ rigidity in torsion making them flexible.
A. Low
B. High
C. Very high
D. Infinitely small
Answer: B
Explanation: Flexible shafts have high rigidity in torsion making then capable to transmit torque.
11. The shaft is always stepped with ________ diameter at the middle portion and __________ diameter at the shaft ends.
A. Minimum, maximum
B. Maximum, minimum
C. Minimum, minimum
D. Zero, infinity
Answer: B
Explanation: Maximum diameter is in the middle portion while it is minimum at the ends.
12.______ is used for a shaft that supports rotating elements like wheels, drums or rope sleaves.
A. Spindle
B. Axle
C. Shaf
D. None of the listed
Answer: A
Explanation: That is axle and not a spindle.
13. Axle is frequently used in torque transmission.
A. True
B. False
Answer: B
Explanation: Axle is a shaft supporting rotating elements
14.Is it necessary for an axle to be ______ with respect to rotating element?
A. Stationary
B. Moving
C. Moving or stationary
D. None of the listed
Answer: C
Explanation: The axle may be stationary or rotate with the element.
15. Counter shaft is a secondary shaft.
A. True
B. False
Answer: A
Explanation: It is a secondary shaft used to counter the direction of main shaft
16. Hot rolling produces a stronger shaft then cold rolling.
A. True
B. False
Answer: B
Explanation: Cold rolling produces stronger shaft as grain structure isn’t deformed in cold working.
17. Shafts are subjected to ______ forces.
A. Compressive
B. Tensile
C. Shear
D. None of the listed
Answer: B
Explanation: Shafts are subjected to tensile forces.
18. Flexible shafts have ______ rigidity in bending moment.
A. High
B. Low
C. Very high
D. Extremely low
Answer: B
Explanation: Flexible shafts have low rigidity in bending moments making them flexible
19. While designing shaft on the basis of torsional rigidity, angle of twist is given by?
A. Ml/Gd⁴
B. 584Ml/Gd⁴
C. 292 Ml/Gd⁴
D. None of the mentioned
Answer: B
Explanation: θ=(180/π)xMl/GJ where J=πd⁴/32.
20. According to the ASME code, maximum allowable shear stress is taken as X% of yield strength or Y% of ultimate strength.
A. X=30 Y=18
B. X=30 Y=30
C. X=18 Y=18
D. X=18 Y=30
Answer: A
Explanation: ASME Standard. The lesser value is taken among the two.
21. Does ASME Standard take into consideration shock and fatigue factors?
A. Yes
B. No
Answer: A
Explanation: Moment is multiplied by a number to consider these factors while designing the shaft
22. A force 2P is acting on the double transverse fillet weld. Leg of weld is h and length l. Determine the shear stress in a plane inclined at θ with horizontal.
A. PSinθ(Sinθ+Cosθ)/hl
B. P(Sinθ+Cosθ)/hl
C. Pcosθ(Sinθ+Cosθ)/hl
D. None of the listed
Answer: A
Explanation: F=PSinθ and width=h/(Sinθ+Cosθ).
23. Maximum shear stress in transverse fillet weld of leg h and length l is
A. P/hl
B. 1.21P/hl
C. P/1.21hl
D. None of the listed
Answer: B
Explanation: τ= PSinθ(Sinθ+Cosθ)/hl, by maximising it θ=67.5’ and hence find corresponding τ.
24. A sunk key fits in the keyway of the _____ only.
A. Hub
B. Sleeve
C. Both hub and sleeve
D. Neither hub nor sleeve
Answer: A
Explanation: Sunk key fits halfway in the hub and halfway in the shaft
25. Hollow saddle key is superior to flat saddle key as far as power transmitting capability is concerned.
A. True
B. False
Answer: B
Explanation: The resistance to slip in case of flat key is more.
26. Saddle key is more suitable than sunk key for heavy duty applications.
A. True
B. False
Answer: B
Explanation: In sunk key, relative motion is also prevented by shear resistance of sunk key and hence sunk key is recommended
27. The main advantage of sunk key is that it is a _____ drive.
A. Positive
B. Negative
C. Neutral
D. None of the listed
Answer: A
Explanation: Sunk key is a positive drive and no slip occurs.
28. Woodruff key permits _____ movement b/w shaft and the hub.
A. Axial
B. Radial
C. Eccentric
D. None of the listed
Answer: B
Explanation: Woodruff key is a sunk key and doesn’t permit axial moment.
29. Determine the length of kennedy key required to transmit 1200N-m and allowable shear in the key is 40N/mm². The diameter of shaft and width of key can be taken as 40mm and 10mm respectively.
A. 49mm
B. 36mm
C. 46mm
D. 53mm
Answer: D
Explanation: l=M/[dbτ√2].
30. Splines are keys.
A. True
B. False
Answer: A
Explanation: Splines are keys made with shafts.
31. Involute splines have stub teeth with a pressure angle of ___
A. 30
B. 45
C. 60
D. Can’t be determined
Answer: B
Explanation: Pressure angle is 30’ and not 60’
32. A coupling is a mechanical device that temporarily joins two rotating shafts to each other.
A. True
B. False
Answer: B
Explanation: A coupling permanently joins two rotating shafts.
33. In distortion energy theorem, if a unit cube is subjected to biaxial stress, then S(yt) is given by which of the following?
A. √ (σ₁²- σ₁σ₂ +σ₂²)
B. σ₁²- σ₁σ₂ +σ₂²
C. √ (σ₁²+ σ₁σ₂ +σ₂²)
D. σ₁²+ σ₁σ₂ +σ₂²
Answer: A
Explanation: S(yt)=√[(σ₁ -σ₂)²+(σ₂ -σ₃)²+(σ₃ -σ₁)²]/2, for σ₃=0; expression a is obtained.
34. Oldham coupling i used to connect two shafts having intersecting axes.
A. True
B. False
Answer: B
Explanation: Oldham coupling is used to connect two parallel shafts separated by a small distance
35. A machine started malfunctioning due to some issues with the coupling. The coupling emplaced in the machine was Oldham. The only coupling available in the workshop is Hooke’s coupling. So Oldham coupling can be replaced by Hooke’s coupling.
A. True
B. False
Answer: B
Explanation: It is not possible to replace Oldham by Hooke’s coupling as Hooke’s is used to connect intersecting axes and not parallel axes shafts.
36. A muff coupling is connecting two shafts. The torque involved is 650N-m. The shaft diameter is 45mm with length and breadth of the key being 14mm and 80mm respectively. Find the shear stress induced in the key.
A. 30.2N/mm²
B. 25.8N/mm²
C. 34.4N/mm²
D. None of the listed
Answer: B
Explanation: τ =2M/dbl
37. The region of safety for biaxial stresses is of which shape in the case of maximum distortion energy theorem.
A. Ellipse
B. Circle
C. Rectangle
D. Square
38. Distortion energy theorem is not recommended for ductile materials.
A. True
B. False
Answer: B
Explanation: Experimental investigations have shown that distortion energy theorem gives good results for failure of ductile component.
39. Among maximum shear stress theory and distortion energy theory, which gives the higher value shear yield strength?
A. Maximum shear stress theory
B. Distortion energy theory
C. Both give equal values
D. Vary from material to material
Answer: B
Explanation: Maximum shear stress theory gives S(sy)=0.5S(yt) while Distortion energy theorem gives S(sy)=0.577(Syt).
40. A muff coupling is connecting two shafts. The torque involved is 650N-m. The shaft diameter is 45mm with length and height of the key being 14mm and 80mm respectively. Find the compressive stress induced in the key.
A. 70.1 N/mm²
B. 51.6N/mm²
C. 45.5N/mm²
D. None of the listed
Answer: B
Explanation: σ=4M/dhl
41. Clamp coupling employ bolts.
A. True
B. False
Answer: A
Explanation: The two halves of sleeve are clamped together by bolts.
42. Entire torque is transmitted by friction in the clamp coupling.
A. True
B. False
Answer: B
Explanation: Some torque is transferred by friction and some by key.
43.Does shaft has to be shifted i axial direction to remove clamp coupling.
A. Yes
B. No
Answer: B
Explanation: Clamp coupling unlike muff coupling is easily removed without shifting the shaft in axial direction
44. If shaft diameter is 40mm, calculate the diameter of sleeves in clamp coupling.
A. 100mm
B. 80mm
C. 60mm
D. 40mm
Answer: A
Explanation: Dia=2.5d.
45. If shaft diameter is 40mm, calculate the length of sleeves in clamp coupling.
A. 80mm
B. 140mm
C. 100mm
D. 120mm
Answer: B
Explanation: L=3.5d
46. If 8 bolts are emplaced in a clamp coupling with shaft diameter 80mm d, calculate the tensile force on each bolt if coefficient of friction is 0.3 and torque transmitted is 4000N-m.
A. 51234.4N
B. 45968.3N
C. 41666.7N
D. None of the listed
Answer: C
Explanation: P=2M/fdn.
47. If 8 bolts are emplaced in a clamp coupling with shaft diameter 80mm d, calculate the diameter of each bolt if coefficient of friction is 0.3 and torque transmitted is 4000N-m. Permissible tensile stress is 80N/mm².
A. 27mm
B. 25mm
C. 23mm
D. 21mm
Answer: A
Explanation: Ax80=2M/fdn.
48. Power is transmitted by only in rigid flange coupling.
A. True
B. False
Answer: B
Explanation: Power is transmitted by key as well as bolts.
49. If shaft diameter is 60mm, how many bolts are recommended for rigid flange coupling?
A. 2
B. 3
C. 4
D. 5
Answer: C
Explanation: If shaft diameter is between 40mm and 100mm, 4 bolts are used.
50. Determine the diameter of the bolts used in rigid flange coupling if transmitted torque is 270N-m, pitch circle diameter=125mm and four bolts are emplace in the coupling. Permissible shear stress in the bolts is 70N/mm².
A. 3.8mm
B. 3.6mm
C. 4.4mm
D. 4mm
Answer: C
Explanation: d²=8M/πDNτ.
51. The hub is treated as a solid shaft while calculating torsional shear stress in the hub.
A. True
B. False
Answer: B
Explanation: Hub is treated as a hollow shaft.
52. Find the shear stress in a flange at the junction of hub in rigid flanged coupling if torsional moment is 2980N-m and diameter of hub being 125mm. Also the thickness of flange is 25mm.
A. 6.77N/mm²
B. 10.24N/mm²
C. 4.84N/mm²
D. 4.22N/mm²
Answer: C
Explanation: τ=2M/πd²t.
53. If shaft diameter is 30mm and number of pins emplaced are 6, then the diameter of the pin will be?
A. 6.4mm
B. 5.6mm
C. 6.1mm
D. 5.9mm
Answer: C
Explanation: d₁=.5d/√N.
54. Calculate the force acting on the each pin in flexible coupling if torque transmitted is 397N-m and PCD=120mm with number of pins 6.
A. 1400.3N
B. 1102.8N
C. 1320.3N
D. None of the listed
Answer: B
Explanation: P=2M/DN.