In a pitot tube measurement, the stagnation pressure is 105.5 kPa and static pressure is 100 kPa. What is the velocity of the fluid? (ρ = 1000 kg/m³)
Answer: A
Using Bernoulli: (P₀ - P) = ½ρV². So V = √(2 × 10005500) = 3.32 m/s ≈ 3.16 m/s
Q.142Easy
A 300 mm diameter pipe reduces to 150 mm diameter. If velocity in the larger pipe is 1.5 m/s, what is the velocity in the smaller pipe, assuming incompressible flow?
Answer: B
By continuity equation A₁V₁ = A₂V₂. Since diameter ratio is 2:1, area ratio is 4:1, so V₂ = 1.5 × 4 = 6.0 m/s
Q.143Medium
A submerged orifice discharges water under a head of 4 m. The coefficient of discharge is 0.62. If the orifice area is 0.01 m², what is the discharge rate?
Answer: A
Q = Cd × A × √(2gh) = 0.62 × 0.01 × √(2 × 9.81 × 4) = 0.0124 m³/s
Q.144Easy
For laminar flow in a circular pipe, the Hagen-Poiseuille equation gives discharge as Q = πΔPd⁴/(128μL). This is valid for Reynolds number:
Answer: B
Hagen-Poiseuille equation applies only to laminar flow where Re < 2300. Beyond this critical value, flow becomes transitional or turbulent.
Q.145Medium
A pump delivers 0.05 m³/s of water against a head of 25 m. If the pump efficiency is 80%, what is the required power input?
A jet of water with velocity 20 m/s hits a flat plate perpendicularly. If the jet diameter is 50 mm and density is 1000 kg/m³, what is the force exerted on the plate?
Answer: A
Force F = ρAV² = 1000 × (π × 0.025²) × 20² = 1000 × 0.001963 × 400 = 3927 N
Q.150Medium
Which dimensionless number is used to characterize the relative importance of gravity and inertial forces in open channel flow?
Answer: B
The Froude number Fr = V/√(gD_h) characterizes gravity effects. In open channel flow, it determines flow regime (subcritical Fr<1, supercritical Fr>1).
Q.151Medium
A 100 mm diameter pipe contains a 90° elbow. If water flows at 3 m/s and minor loss coefficient K = 0.9, what is the head loss?
Answer: C
h_minor = K(V²/2g) = 0.9 × (199.62) = 0.369 m
Q.152Easy
In compressible flow, if Mach number M = 1.2, the flow is classified as:
Answer: C
Mach number classification: M < 1 (subsonic), M = 1 (sonic), 1 < M < 5 (supersonic), M > 5 (hypersonic). M = 1.2 is supersonic.
Q.153Hard
A vertical pipe of diameter 40 mm has water flowing upward at 2.5 m/s. If the friction factor is 0.035 and pipe length is 50 m, what is the total head loss (friction + elevation)?
Answer: C
h_f = 0.035 × (050.04) × (6.1925.62) = 1.12 m; total = 1.12 + 50 = 51.12 m
Q.154Hard
A circular jet impinges on a 45° inclined flat plate and splits equally. If jet velocity is 15 m/s and diameter is 30 mm, what is the magnitude of the resultant force?
Answer: C
Using momentum equation with 45° deflection, the resultant force = ρAV² × √2 = 1000 × 0.000707 × 225 × 1.414 = 2648 N
Q.155Hard
In a venturi meter, if the area ratio is 4:1 and the pressure difference is 8 kPa, what is the velocity in the throat? (ρ_water = 1000 kg/m³)
Answer: B
From Bernoulli and continuity: V₂ = √(2ΔP/(ρ(A₁²/A₂² - 1))) = √(16000/(1000 × 15)) = 4.12 m/s
Q.156Hard
A horizontal jet of 0.02 m² cross-section with velocity 8 m/s strikes a curved vane and is deflected 60°. What is the force on the vane in the direction of jet?
Answer: C
Force = ρAV²(1 - cos60°) = 1000 × 0.02 × 64 × 0.5 = 6.4 kN. The deflection angle affects the force component.
Q.157Medium
For a rectangular open channel with width 5 m carrying 12 m³/s of water, if the critical depth is 1.5 m, what is the critical velocity?
Answer: C
Critical velocity V_c = √(gD_c) = √(9.81 × 1.5) = 3.84 m/s. Alternatively Q/A = 12/(5×1.5) = 1.6 m/s. Using V_c² = g × D_h gives the correct answer.
Q.158Easy
In fluid mechanics, which of the following statements about Pascal's law is correct?
Answer: A
Pascal's law states that pressure applied to a confined fluid is transmitted undiminished in all directions. This principle is fundamental to hydraulic systems used in Indian industries.
Q.159Easy
The continuity equation for incompressible flow states that A₁V₁ = A₂V₂. If water flows through a pipe that narrows from 100 mm to 50 mm diameter, the velocity ratio V₂/V₁ is:
Answer: C
Using continuity equation: A₁V₁ = A₂V₂. Area ratio = (D₁/D₂)² = (50100)² = 4. Therefore V₂/V₁ = 4:1. This is critical for pipe flow analysis in water supply systems.
Q.160Easy
According to Bernoulli's equation, which energy form is neglected when the fluid flow is at constant elevation in a horizontal pipe?
Answer: B
In Bernoulli's equation (P/ρg + V²/2g + Z = constant), when flow is in a horizontal pipe at constant elevation, Z (potential energy head) remains constant and can be neglected in differential form.
