Quiz: Mechanical Engineering 11th June

Quiz: Mechanical Engineering
Exam:  AE/JE
Topic: Miscellaneous

Each question carries 1 mark
Negative marking: 1/4 mark
Time: 10 Minutes

Q1. Which one of the following gear tooth failures is induced when maximum Hertz contact stress on gear tooth surface exceeds surface endurance strength of tooth?

(a). Abrasive strength
(b). Corrosive wear
(c).  Galling
(d). Destructive pitting

Q2. If (σ_b x Y)_pinion > ( σ_b  x Y)_gear , ________ is designed for bending.

(a). gear    
(b). pinion
(c). both a. and b.
(d). none of the above

Q3. To avoid interference the minimum number of teeth required on helical pinion decreases as pressure angle ________

(a). increases
(b). decreases
(c). does not affect number of teeth
(d). none of the above

Q4. Load acting on bearing in its plane of rotation is called as __________

(a). radial load
(b). Axial load
(c). thrust load
(d). none of the above

Q5. V-belts follows

(a). Have low reduction ratio
(b). Due to wedging action slip is negligible
(c). Transmits power over long center distances
(d). All of the above

Q6. Which of the following formula is used to calculate minimum oil-film thickness in hydrodynamic bearings?  

(a). h = (c + Є)
(b). h = (c – Є)
(c). h = c (1+ Є)
(d). h = c (1- Є)

Q7. The ratio of effective length and least lateral dimension for short column is _______

(a). < 12
(b). >12
(c). ≥ 12
(d). none of the above

Q8.Principal stress is the magnitude of which stress acting on the principal plane.
(a).  Shear stress
(b). Normal stress
(c). Both a. and b.
(d). None of the above

Q9. St. Venant’s theory is also known as maximum _________

(a). principal stress theory
(b). shear stress theory
(c). strain energy theory
(d).  principal strain theory

Q10. What is the bulk modulus of a material, if a cube of 90 mm changes its volume to 4000 mm³ when subjected to compressive force of 2.0 x 10⁶ N?
(a). 248 Gpa
(b). 65 Gpa
(c). 67.5 Gpa
(d). 70 Gpa

Solutions

S1. Ans.(d)

Sol. Destructive pitting generally results from surface overload conditions which cannot be alleviated by initial pitting. Destructive pitting can be avoided by keeping the load on the surface below the endurance limit for the material.

S2. Ans.(a)

Sol. (σ_b x Y)_pinion > ( σ_b  x Y)_gear 

Gear will be designed on the basis of weaker element between gear and pinion according to Lewis equation.

S3. Ans.(a)

Sol. Minimum number of teeth on the pinion (TP) in order to avoid interference may be obtained from the following relation:
where

AW = Fraction by which the standard addendum for the wheel should be multiplied,

G = Gear ratio or velocity ratio = TG / TP = DG / DP,

φ = Pressure angle or angle of obliquity.

S4. Ans.(a)

Sol.

S5. Ans.(b)

Sol.

S6. Ans.(d)

Sol. The eccentricity ratio is defined as ratio of eccentricity and radial clearance.
∈=e/c…….(1.1)
Where ∈is the eccentricity ratio.
R=e+r+ho……..(1.2)
From equation 1.1 and 1.2
C=R-r =e+ho=c∈+ho
Or c(1-∈)=ho
Ho= minimum oil film thickness(in mm)

S7. Ans.(a)

Sol. For short column Ratio of gauge length to minimum radius of gyration is <12

For long column Ratio of gauge length to minimum radius of gyration is >12

S8. Ans.(b)

Sol. Principal stresses are the maximum and minimum normal stresses on a particular plane, on which shear stresses are zero.

S9. Ans.(d)

Sol.

 Maximum principal stress theory                                (Rankine’s theory)

• Maximum shear stress theory                              (Coulomb, Tresca and Guest’s theory)
• Distortion energy theory                                       (Huber von Mises and Henky’s theory)
• Maximum strain theory                                          (St. Venant’s theory)
• Maximum total strain energy theory                      (Haigh’s theory)

S10. Ans.(a)
Sol. Given,
a=90 mm
V_1=〖90〗^3
=729000 〖mm〗^3
V_2=4000 〖mm〗^3
∆V=729000-4000
=725000 〖mm〗^3
Bulk modulus k=-∆p/(∆V/V)=-(F/A)/(∆V/V)= ((2×10^6)/(90^3))/(725000/(90^3)) =248 Gpa

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