Question

A one-meter deep and sheet-like waterflow on a sandy beach developed antidunes. The minimum velocity of the waterflow was _______m/s. (Round off to two decimal places) (Use g = 10 m/s²)

Answer 1

Correct Answer: 3.1

Given:
Water depth \(h=1\ \text{m}\). Use \(g=10\ \text{m/s}^2\). Antidunes occur when flow is at least critical (Froude number \(Fr \ge 1\)). The minimum velocity corresponds to the critical condition \(Fr=1\).  
Froude number: \[ Fr=\frac{U}{\sqrt{g h}}. \] Set \(Fr=1\) so \(U=\sqrt{g h}\). 
Compute: \[ U=\sqrt{10\times 1}=\sqrt{10}\approx 3.16227766\ \text{m/s}. \] Rounded to two decimals: \[ \boxed{U = 3.16\ \text{m/s}} \]