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# UPPSC Lec’21 ME: Daily Practices Quiz. 30-Sep-2021

Quiz: Mechanical Engineering
Exam: UPPSC Lecturer
Topic: Miscellaneous

Each question carries 1 mark
Negative marking: 1/4 mark
Time: 6 Minutes

Q1. If the radius is doubled and the speed is reduced to half of its original value, the centrifugal force would be:
(a) 2.0 times the original value
(b) 0.5 times the original value
(c) 0.2 times the original value
(d) 0.1 times the original value

Q2. As compared to the mass of a body on the earth, its mass on the moon will be
(a) 6 times higher
(b) 6 times lower
(c) √6 times higher
(d) None of these

Q3. A solid circular shaft is subjected to pure torsion. The ratio of maximum shear stress to maximum normal stress at any point would be
(a) 1 : 1
(b) 1 : 2
(c) 2 : 1
(d) 2 : 3

Q4. Two material of shafts A and B are same, and A is thrice the diameter of B. The torque that can be transmitted by A is
(a) 3 times that of B
(b) 27 times that of B
(c) 9 times that of B
(d) 81 times that of B

Q5. In case of biaxial state of stress, normal stresses are σ_x=400 N/mm². σ_y=100 N/mm² and shear stress τ = 200 N/mm². The maximum principal stress is
(a) 800 N/mm²
(b) 900 N/mm²
(c) 500 N/mm²
(d) 1200 N/mm²

Q6. Surface defects are
(a) Grain boundaries
(b) Tilt boundary
(c) Twin boundary
(d) All of these

### Solution

S1. Ans. (b)
Sol.
F_2/F_1 =m_2/m_1 ×(ω_2/ω_1 )^2×r_2/r_1
=(1/2)^2×2=2/4=0.5 (∵ m_1=m_2)

S2. Ans. (d)
Sol. On moon only acceleration due to gravity is one sixth of acceleration due to gravity on earth.
g^’=g/6
So, weight of the body on moon becomes one sixth of the weight of the body on earth.
But there is no change in mass.

S3. Ans.(a)
Sol.
T_e=√(M^2+ T^2 )
For pure torsion M = 0
T_e=T
(πd^3)/16.τ_max=T
and M_e=1/2 [ M+√(M^2+T^2 )]
M_e=T/2
(πd^3)/32.σ_max=T/2
∴τ_max/σ_max =1∶1

S4. Ans.(b)
Sol.
Material of both shafts is same i.e., τ_perm is same
∴T ∝d^3
T_A/T_B =(d_A^3)/(d_B^3 )=3^3/1^3 =27
∴T_A=27T_B

S5. Ans.(c)
Sol.
σ_x=400 MPa;
σ_y=100 MPa
and,τ_xy=200 MPa
σ_1=1/2 [(σ_x+σ_y )+√((σ_x-σ_y )^2+4τ_xy^2 )]
=1/2 [500+√(300^2+4×200^2 )]
σ_1=(500+500)/2
=500 MPa = 500 N/mm²

S6. Ans. (d)
Sol.
Point Defects
Vacancies
Interstitial atoms
Impurities
Line Defects
Edge dislocation
Screw dislocation
Surface or Grain boundaries defects
Grain boundaries
Tilt boundary
Twin boundary
Twist boundary
Volume defects
Stacking faults

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