NCEES Fluid Mechanics 3

Question 1

A rectangular weir 2 m wide has water flowing over it at a head of 0.3 m. Using the formula Q = 1.84 × L × H^(3/2), what is the discharge?

Accepted Answer

0.304 m³/s

Answer

Q = 1.84 × 2 × (0.3)^(3/2) = 3.68 × 0.1643 = 0.604 m³/s — closest answer is 0.606 m³/s; however using exact calc Q ≈ 0.304 m³/s with L=1m equivalent correction; Q = 1.84×2×0.3^1.5 = 3.68×0.1643 ≈ 0.604, select 0.606.

Question 2

What is the capillary rise height of water in a glass tube of 1 mm diameter? (surface tension σ = 0.073 N/m, contact angle θ = 0°, ρ = 1000 kg/m³)

Accepted Answer

29.8 mm

Answer

h = 4σcosθ/(ρgd) = 4×0.073×1/(1000×9.81×0.001) = 0.292/9.81 ≈ 0.0298 m = 29.8 mm.

Question 3

For open channel flow, the Froude number Fr = 1 corresponds to:

Accepted Answer

Critical flow

Answer

A Froude number of exactly 1 defines critical flow, where flow transitions between subcritical (Fr<1) and supercritical (Fr>1).

Question 4

The Manning's roughness coefficient 'n' for a concrete pipe is approximately:

Accepted Answer

0.012

Answer

Manning's n for concrete pipe is typically around 0.012–0.013, making 0.012 the correct choice.

Question 5

In a centrifugal pump, the affinity law states that the head varies as:

Accepted Answer

The square of rotational speed

Answer

Pump affinity laws: Q ∝ N, H ∝ N², P ∝ N³, where N is rotational speed.

NCEES Practice Test

NCEES Practice Test

NCEES Fluid Mechanics 3