MCQs on Shaft Design

1 - Question

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

Explanation: θ=(180/π)xMl/GJ where J=πd⁴/32.

2 - Question

According to 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

Explanation: ASME Standard. The lesser value is taken among the two.

3 - Question

Does ASME Standard take into consideration shock and fatigue factors?
a) Yes b) No

Explanation: Moment is multiplied by a number to consider these factors while designing the shaft.
Figure 1

The layout of a shaft supported on bearings at A & B is shown. Power is supplied by means of a vertical belt on pulley B which is then transmitted to pulley C carrying a horizontal belt. The angle of wrap is 180’ and coefficient of friction is 0.3. Maximum permissible tension in the rope is 3kN. The radius of pulley at B & C is 300mm and 150mm.
For questions 4-7, refer to figure 1.

4 - Question

Calculate the torque supplied to the shaft.

a) 453.5N-m
b) 549.3N-m
c) 657.3N-m
d) None of the listed

Explanation: M=(P₁-P₂)xR where P₁=3000N, P₂=P₁/e^(Coeff of friction x Angle of wrap).

5 - Question

Calculate the tension in the rope of pulley C.

a) 6778.3N and 7765.3N
b) 5948.15N and 2288.75N
d) None of the listed

Explanation: (P₃-P₄)x150=549.3×1000 and P₃/P₄=2.6. Hence P₃=5948.15N and P₄=2288.75N.

6 - Question

If allowable shear stress in the shaft is 70N/mm² and torsional and bending moments are M=1185000N-mm and m=330000N-mm, find the diameter of the shaft.

a) 36.8mm
b) 39.7mm
c) 44.7mm
d) 40.3mm

Explanation: 70=(16/πdᵌ)x√M²+m².

7 - Question

If bending moment on point B in horizontal plate is M and in vertical plane is m, then the net bending moment at point B is?

a) M
b) m
c) M+m
d) √M²+m²

Explanation: The two moments act perpendicularly to each other.

8 - Question

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

Explanation: d⁴=584Ml/Gθ.

9 - Question

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

Explanation: 0.18×400.

10 - Question

The stiffness of solid shaft is more than the stiffness of hollow shaft with same weight.

a) True
b) False

Explanation: Hollow shaft is more stiff.

11 - Question

The strength of hollow shaft is more than the strength of solid shaft of same weight.

a) True
b) False

Explanation: Outer fibers are more effective in resisting the applied moments. In hollow shafts material is removed and spread on a larger radius.

12 - Question

Solid shaft is costlier than hollow shaft of same weight.

a) True
b) False

Explanation: Hollow shaft cost is more as material is to be selectively emplaced.

13 - Question

Solid shafts are used in epicyclic gearboxes.

a) True
b) False

Explanation: In epicyclic gears, one shaft rotates inside other and hence hollow shafts are used.

14 - Question

Flexible shafts have ___ rigidity in torsion making them flexible.

a) Low
b) High
c) Very high
d) Infinitely small

Explanation: Flexible shafts have high rigidity in torsion making then capable to transmit torque.

15 - Question

Flexible shafts have ______ rigidity in bending moment.
a) High b) Low c) Very high d) Extremely low