Quiz: Civil Engineering 7 Nov 2020

Quiz: Civil Engineering
Exam: RSMSSB-JEn
Topic: Fluid Mechanics

Each question carries 1 mark
Negative marking: 1/3 mark
Time: 10 Minutes

Q1. Pseudo plastic fluids are
(a) Shear rate thinning
(b) Shear rate thickening
(c) Time depended
(d) Both shear rate thinning and time dependent

Q2. In a rectangular open channel for the critical flow across at 2m depth of flow the specific energy at this depth will be
(a) 1m
(b) 2m
(c) 3m
(d) 4m

Q3. Which of the following statement is correct?
(a) Pumps connected in parallel are used to boost the head, whereas pumps operating in series boosts their discharge
(b) Pump operating in series, boost the head, whereas pump operating in parallel, boost the discharge
(c) Pump either in parallel or series always boost only discharge
(d) Pump either in parallel or series always boost only head

Q4. If a pipe of diameter 30 cm running full of water with velocity 100 m/sec is changed by a pipe of diameter 15 cm, then the velocity of water flowing through the pipe will be
(a) 50 m/sec
(b) 25 m/sec
(c) 200 m/sec
(d) 400 m/sec

Q5. By which one of the following a small quantity of water may be lifted to a great height?
(a) Hydraulic ram
(b) Hydraulic crane
(c) Hydraulic lift
(d) Hydraulic coupling

Q6. M^(-2) LT^(-2) could be the dimensions of
(a) Pressure
(b) Acceleration
(c) Discharge
(d) Specific weight

Q7. If the velocity of the flow is 2.5 m/s and the cross-sectional area of a rectangular channel is 12m² then what amount of discharge it can carry :
(a) 30 m³
(b) 25 m³
(c) 40 m³
(d) 35 m³

Q8. A stream function is
(a) defined only for incompressible flow
(b) defined for irrotational flow
(c) defined when the flow is continuous
(d) defined only for steady flow

Q9. The critical depth of flow in a most economical triangular channel section for a discharge of 1 m³/sec is given by
(a) (1/9.8)^(1/5)metre
(b) (1/9.8)^(1/3)metre
(c) (1/4.9)^(1/5)metre
(d) (1/4.9)^(1/3)metre

Q10. The pressure at the summit of a syphon is
(a) equal to atmospheric
(b) less than atmospheric
(c) more than atmospheric
(d) None of the above

SOLUTIONS
S1. Ans.(a)
Sol. Pseudoplastic fluids are shear thinning fluids. The viscosity of these fluids decreases as the shear rate increases.
Ex. Paints, nail polish, ketchup etc.

S2. Ans.(c)
Sol. Given, Critical depth of flow (y_c) = 2m.
Specific energy (E_C )= ?
Specific energy for rectangular open channel is given by –
E_c=3/2 Y_c
=3/2×2
▭(E_C=3 m)

S3. Ans.(b)
Sol. When two pumps are operated in series then discharge remains same and head produced is doubled while if they operated in parallel then discharge is doubled and head remains the same.

S4. Ans.(d)
Sol. Given,
d_1=30 cm
V_1=100 m\/sec⁡
d_2=15 cm
V_2= ?
By continuity equation
A_1 V_1=A_2 V_2
π/4 (d_1 )^2×100=π/4 (d_2 )^2×V_2
(30)^2×100=(15)^2×V_2
▭(V_2=400 m\/sec )

S5. Ans.(a)
Sol. The hydraulic ram is a type of pump in which the energy of large quantity of water falling through small height is utilized to lift a small quantity of water to a great height.

S6. Ans.(d)
Sol.
Quantity                      Dimension
Pressure                      ML^(-1) T^(-2)
Acceleration               LT^(-2)
Discharge                   L^3 T^(-1)
Specific Weight         M^(-2) LT^(-2)

S7. Ans.(a)
Sol. Given, Velocity of flow (V) = 2.5 m/sec.
Area (A) = 12 m²
Discharge (Q) = ?
Q=A.V
=12×2.5
=30 m³\/sec

S8. Ans.(a)
Sol. A stream function is defined only for incompressible flow. In stream function, the partial derivative with respect to any direction will give the velocity component at right angle to that direction.

S9. Ans.(c)
Sol. for most economical triangular channel section, the side slope m = tanθ = tan 45
▭(m=1)
Given, Q = 1 m³/sec.
Now, critical depth for triangular channel
Section –
y_c=((2Q^2)/(gm^2 ))^(1\/5)
=[(2×(1)^2)/(9.8×(1)^2 )]^(1\/5)
▭(y_c=(1/4.9)^(1\/5) metre)

S10. Ans.(b)
Sol. Syphon is long bent pipe which is used to transfer liquid from a reservoir at its higher elevation to another reservoir at a lower level. The flow through the syphon is only possible if the pressure at summit point is less than the atmospheric pressure.

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