Quiz: Civil Engineering 23 Oct 2020

Quiz: Civil Engineering
Exam: SSC-JE
Topic: Fluid Mechanics

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

Q1. Capillary rise is maximum for
(a) coarse grained soils
(b) find grained soils
(c) will graded soils
(d) gap graded soils

Q2. The viscosity of a fluid with specific gravity 1.3 is measured to be 0.0034 N-sec./m². Its kinetic viscosity, in m²/s, is
(a) 2.6 × 10–6
(b) 4.4 × 10–6
(c) 5.8 × 10–6
(d) 7.2 × 10–6

Q3. Specific speed of a centrifugal pump is
(a) (N√Q)/H
(b) (N√H)/Q
(c) (N(H)^(3/4))/√Q
(d) None of these

Q4. The force of attraction between the individual particles bound together is known as
(a) Dilatancy
(b) Adhesive
(c) Cohesion
(d) Internal friction

Q5. A two-dimensional flow field is given by stream function Ψ = x² – y². The magnitude of absolute velocity at a point (1,1)
(a) 2
(b) 4
(c) 8
(d) 2√2

Q6. The centre of gravity of the volume of liquid displaced is called
(a) centre of pressure
(b) centre of buoyancy
(c) metacentre
(d) none of these

Q7. The alternate depths at a section in a rectangular channel are 0.4 m and 1.6 m respectively. The specific energy at the section is
(a) 1.68 m
(b) 1.00 m
(c) 0.64 m
(d) 0.41 m

Q8. The Chezy’s and Manning’s formulae are related by
(a) C=1/n R^(1/6)
(b) C=nR^(1/6)
(c) C=〖Rn〗^(1/6)
(d) C=1/R n^(1/6)

Q9. In two dimensional flow, the equation of a streamline is given as
(a) dy/u=dx/v
(b) dx/u=dy/v
(c) dx/dt=u,dy/dt=v
(d) u/dx=dy/v

Q10. Spherical shape of droplets of mercury is due to
(a) high density
(b) high surface tension
(c) high adhesion
(d) high cohesion

SOLUTIONS

S1. Ans.(b)
Sol. Height of capillary rise in a tube is given by
▭(h=σcosθ/(dγ_(w ) ))
▭(h∝1/d)
So, for fine grained soil effective size ‘d’ is smaller so it will experience more capillary rise.

S2. Ans.(a)
Sol. Given, Dynamic viscosity (μ)=0.0034 (N-sec)/m^2
Specific gravity (G)=1.3
We know,
G=(densityi of fluid(ρ))/(Density of water(ρω) )
1.3=ρ/1000
▭(ρ=1300 kg\/m^3 )
Kinematic viscosity (ν)=(Dynamic viscosity (μ))/Density(ρ)
=0.0034/1300
ν=2.615×10^(-6) m^2/Sec

S3. Ans.(d)
Sol. Specific speed of a centrifugal pump is given by-
▭(N_s=(N√Q)/(H_m )^(3\/4) )
Where N_s= specific speed
N= Rotating speed rpm
Q= Capacity at optimum efficiency
H_m= Total head developed at optimum efficiency point

S4. Ans.(b)
Sol. Adhesion → It is an attractive force between different kind of fluid molecules.
Cohesion → It is an attractive force between same kind of fluid molecules.

S5. Ans.(d)
Sol. given, stream function Ψ = (x²-y²)
Magnitude of absolute velocity at point (1, 1) = ?
Now,
V_x=∂Ψ/∂y
V_x= -2y
▭(〖V_x〗_((1,1) )= -2)
V_y=(-∂Ψ)/∂x
V_y= -2x
▭(〖V_y〗_1,1= -2)
V=√((V_x )^2+(V_y )^2 )
=√((-2)^2+(-2)^2 )
=√8
▭(V=2√2)

S6. Ans.(b)
Sol. When a body is partially or completely submerged in fluid then it experiences a force in vertical upward direction called as buoyancy force and the center of gravity of the volume of liquid displaced is called center of buoyance.

S7. Ans.(a)
Sol. Given, alternate depths
y_1=0.4 m.
y_2=1.6 m.
Specific energy is given by
▭(E=(y_1^2+y_1 y_2+y_2^2)/(y_1+y_2 ))
E=((0.4)^2+(0.4×1.6)+(1.6)^2)/(0.4+1.6)
=3.36/2
▭(E=1.68 m)

S8. Ans.(a)
Sol. The relation between manning’s and chezy’s coefficient are
▭(C=1/n R^(1\/6) )
C = Chezy’s coefficient
n = manning’s coefficient
R = Hydraulic radius

S9. Ans.(b)
Sol. In three dimensional flow, the equation of a streamline is given by –
▭(dx/u=dy/v=dz/w)
For 2D flow,
▭(dx/u=dy/v)

S10. Ans.(b)
Sol. Spherical shape of droplets of mercury is due to high surface tension because due to surface tension, it will try to minimize its surface area and mathematically sphere has minimum surface area.

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