Which of the following dimensionless numbers represents the ratio of inertial forces to viscous forces in fluid flow?
Answer: B
Reynolds number (Re) = inertial forces/viscous forces. It is the fundamental dimensionless number in fluid mechanics.
Q.22Easy
In a horizontal pipe flow, the pressure drop increases with which of the following factors?
Answer: C
Pressure drop (Δp) is proportional to friction factor which increases with pipe roughness. From Hagen-Poiseuille and Darcy equations, rougher pipes cause higher friction losses.
Q.23Easy
A centrifugal pump has an impeller diameter of 0.3 m rotating at 1500 RPM. Calculate the peripheral speed of the impeller tip.
The net positive suction head (NPSH) available is 4.5 m and NPSH required is 3.2 m for a pump. What can be concluded?
Answer: B
Cavitation occurs when NPSH available < NPSH required. Here 4.5 > 3.2, so cavitation is prevented and pump operates safely.
Q.25Easy
Which pump characteristic curve represents the relationship between head and flow rate?
Answer: A
The H-Q (head vs flow rate) curve is the primary pump characteristic curve that shows how head decreases as flow rate increases.
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Q.26Easy
In compressible flow through a nozzle, sonic or critical conditions occur when Mach number equals:
Answer: B
Critical or sonic conditions occur at Mach number = 1.0, where velocity equals the speed of sound in the fluid.
Q.27Easy
In a fluid flow system, which of the following best represents the Bernoulli equation?
Answer: B
Bernoulli equation in head form: P/ρg + V²/2g + Z = constant. Option A is energy form, C is Darcy-Weisbach, D is modified form.
Q.28Easy
The Reynolds number for a fluid flow is defined as the ratio of inertial forces to viscous forces. For a pipe flow with diameter 0.05 m, velocity 2 m/s, and kinematic viscosity 1.0×10⁻⁶ m²/s, calculate the Reynolds number.
Answer: A
Re = (V×D)/ν = (2×0.05)/(1.0×10⁻⁶) = 0.1/(1.0×10⁻⁶) = 100,000
Q.29Easy
Which of the following statements about laminar flow in a circular pipe is correct?
Answer: B
In laminar flow through circular pipes, the velocity distribution follows Hagen-Poiseuille flow with parabolic profile. Maximum velocity is at the centerline (V_max = 2×V_avg), and velocity is zero at the wall (no-slip condition).
Q.30Easy
A fluid flows through a horizontal pipe of diameter 0.1 m at a velocity of 3 m/s. If the pipe suddenly contracts to 0.05 m diameter, what is the velocity in the contracted section (assuming incompressible flow)?
The friction factor 'f' in the Darcy-Weisbach equation depends on Reynolds number and relative roughness. For laminar flow (Re < 2300), friction factor is given by:
Answer: A
For laminar flow in circular pipes, the Hagen-Poiseuille solution gives f = 64/Re. This is independent of roughness and applies for Re < 2300.
Q.32Easy
A manometer shows a pressure difference of 50 mm of mercury (ρ_Hg = 13,600 kg/m³). What is the equivalent pressure difference in Pa?
Answer: A
ΔP = ρ_Hg × g × h = 13,600 × 9.81 × 0.05 = 6,667 Pa
Q.33Easy
For a fluid flowing over a submerged object, the drag force is given by F_D = (21)ρV²AC_D. If velocity doubles and drag coefficient remains constant, drag force increases by a factor of:
Answer: B
F_D ∝ V². When V doubles (V₂ = 2V₁), F_D increases by factor of (2)² = 4
