For a flow in a rectangular channel, the flow velocity is 15 m/s. For a depth of flow of 0.4 m, Froude’s number will be (Take value of acceleration due to gravity (g) to be 10 m/sec²)
- A8.5
- B7.5Correct
- C9.5
- D6.5
Solution
Concept
Froude number of a rectangular channel
Formula
Fr = V / √(g y)
Step-by-step solution
1. Fr = V / √(g y) = 15 / √(10 × 0.4). 2. √4 = 2, so Fr = 15 / 2 = 7.5.
Explanation
For a rectangular channel the hydraulic depth equals the flow depth, so Fr = V/√(gy). A value above 1 shows supercritical flow.
Shortcut
g·y = 4 → √4 = 2 → 15/2.
Common mistake
Using g = 9.81 and approximating, or squaring the denominator.
Correct answer: B) 7.5