Question

What is the approximate unit weight of water used in hydraulic calculations?

• A. $9.81 \, \text{kN/m}^3$
• B. $1.0 \, \text{kN/m}^3$
• C. $100 \, \text{kN/m}^3$
• D. $0.98 \, \text{kN/m}^3$

Hint:

Remember: Water → $9.81 \, \text{kN/m}^3$ (standard value).

Answer 1

The Correct Option is A

Concept: Unit weight ($\gamma$) is defined as the weight per unit volume of a substance.
Step 1: Formula for unit weight.
\[ \gamma = \rho g \]
Step 2: Substitute values for water.
\[ \rho = 1000 \, \text{kg/m}^3, \quad g = 9.81 \, \text{m/s}^2 \] \[ \gamma = 1000 \times 9.81 = 9810 \, \text{N/m}^3 = 9.81 \, \text{kN/m}^3 \]
Step 3: Evaluating the options.

• $9.81 \, \text{kN/m}^3$ $\rightarrow$ Correct
• $1.0 \, \text{kN/m}^3$ $\rightarrow$ Incorrect
• $100 \, \text{kN/m}^3$ $\rightarrow$ Incorrect
• $0.98 \, \text{kN/m}^3$ $\rightarrow$ Incorrect

Step 4: Conclusion.
Thus, the unit weight of water is approximately $9.81 \, \text{kN/m}^3$.