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# Quiz: Mechanical Engineering 1st July

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

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

Q1. The crystal structure of brass is
(a) FCC
(b) BCC
(c) HCP
(d) Orthorhombic

Q2. Which is false statement about properties of aluminium?
(a) Modulus of elasticity is fairly low
(b) Wear resistance is very good
(c) fatigue strength is not high
(d) corrosion resistance is good

Q3. The packing factor of diamond cubic crystal structure is
(a) 90%
(b) 45%
(c) 34%
(d) None of these

Q4. What is the dynamic viscosity in Pa-s for a liquid having relative density of 0.9 and kinematic viscosity of 3 centistoke?
(a) 2.225 x 10^(-3)
(b) 2.7 x 10^(-3)
(c) 1.925 x 10^(-3)
(d) 2 x 10^(-3)

Q5. The work done (in Joule) in blowing a soap bubble of diameter 7 cm. Assume the surface tension of soap solution =0.01 N/m
(a) 30.7 x 10^(-4)
(b) 3.07 x 10^(-4)
(c) 0.307 x 10^(-4)
(d) 3.07 x 10^(-3)

Q6. In order to increase sensitivity of U-tube manometer, one leg is usually inclined by angle θ.If angle θ increases from 30° to 60° then % decrease in the sensitivity of manometer.
(a) 40%
(b) 35%
(c) 43%
(d) 50%

Q7. If a body is drowned in water, it is observed that 20% of the body is above the level of water, then the density of body in kg/m^3is
(a) 200
(b) 400
(c) 800
(d) Data insufficient

Q8. If in an orifice-meter, the diameter of vena-contracta is 20 mm and diameter of orifice is 40 mm, then coefficient of contraction of orifice-meter is
(a) 0.5
(b) 4
(c) 0.25
(d) 2

Q9. In case of power screws, what is the combination of materials used for the screw and the nut?
(a) Cast iron screw and mild steel nut
(b) Carbon steel screw and phosphorous bronze nut
(c) Cast iron screw and cast-iron nut
(d) Aluminium screw and alloy steel nut

Q10. The size of the weld in butt welded joint is equal to
(a) 0.5 X Throat of weld
(b) Throat of weld
(c) √2 X Throat of weld
(d) 2 X Throat of weld

Solutions

S1. Ans (a)
Sol. Crystal structure of brass is Face centered cubic (FCC). In this structure, one atom is situated at each corner of the unit cell along with one atom at each face of it.

S2. Ans (b)
Sol. There are following properties of aluminium-
Good corrosion resistance due to oxide film formation.
Low fatigue strength because of high ductility.
Modulus of elasticity is low.
Poor wear resistance due to low hardness.
Good thermal and electrical conductivity.

S3. Ans (c)
Sol. Atomic packing factor=(Total volume of atoms)/(Volume of unit cell)
Atomic packing factor of Body cantered tetragonal (BCT) Diamond is 0.34.

S4. Ans (b)
Sol. Given,
Kinematic viscosity (ϑ)= 3 centistoke
Density= 0.9×1000=900 kg/m^3
We know, Kinematic viscosity (ϑ)=μ/ρ
Dynamic viscosity (μ)= ϑ. Ρ
μ=3 x 10^(-2)x10^(-4)x900
μ=2.7 x 10^(-3) Pa-s

S5. Ans (b)
Sol.

There are two exposed surfaces of soap bubble as shown in figure.
We know,
Work done in blowing up a soap bubble (W)=Surface tension (σ) x Surface area (A)
W= σ x 4πr^2 x 2
W=0.01 x 4π〖(3.5)〗^2 x 2 x 10^(-4)
W=3.07 x 10^(-4) Joule

S6. Ans (c)
Sol. If θ is angle of inclination,
Sensitivity of inclined manometer(S)=1/sinθ
If θ=30°
Then Sensitivity (S_(θ=30))= 1/sinθ=1/sin30=2
If θ=60°
Then Sensitivity (S_(θ=60))= 1/sinθ=1/sin60=2/√3
% Decrease in sensitivity=(S_(θ=30)-S_(θ=60))/S_(θ=30) =(2-2/√3)/2×100=42.26% or 43%

S7. Ans (c)
Sol. We know that
From Archimedes’ principle,
Weight of the floating body=weight of the liquid displaced
If x part of the body is in the liquid, volume of the body is V, Density of water is ρw, Density of body is ρ_b , then x.V.ρ(w.)g = V.ρb.g 0.8 x ρ(w.)= ρ_b
ρ_b= 0.8 x 1000
ρ_b=800 kg/m^3

S8. Ans (c)
Sol. We know that
Coefficient of contraction (C_c)=(Area of vena-contracta〖(A〗_c))/(Area of orifice〖(A〗_o))
C_c=(d_c^2)/(d_o^2 )=20^2/40^2
C_c=1/4=0.25

S9. Ans (b)
Sol. Screw is made of Carbon steel and Nut is made of phosphorus bronze or cast iron (for low speed).

S10. Ans (b)
Sol. For Butt weld joint,
Size of weld=throat of weld=thickness of plate

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