The hydrostatic equation holds not just for air, but for other fluids such as water (air, though it is a gas, is often referred to as a 'fluid') as well. In the case of water the equation becomes even easier, as water (as opposed to air) can be treated as incompressible, meaning the density is constant. Use a value of 1000 kilogram per cubic metre as density.

Using this information, compute the local pressure (in [Pa]) at 2.5 metres depth in a swimming pool situated at 2400 metres altitude in the mountains. Assume a standard atmosphere.

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To calculate the local pressure at a depth of 2.5 meters in a swimming pool located at an altitude of 2400 meters, we will use the hydrostatic pressure equation:

\[ P = P_0 + \rho g h \]

Where:

  • \( P \) is the total pressure at depth.
  • \( P_0 \) is the atmospheric pressure at altitude (in pascals).
  • \( \rho \) is the density of the fluid (for water, \(\rho = 1000 , \text{kg/m}^3\)).
  • \( g \) is the acceleration due to gravity (approximately \( 9.81 , \text{m/s}^2\)).
  • \( h \) is the depth of the fluid (in meters).

Step 1: Calculate the atmospheric pressure at 2400 meters

The standard atmospheric pressure at sea level is approximately \( 101325 , \text{Pa} \). However, the pressure decreases with altitude. The atmospheric pressure can be approximated at a certain altitude using the barometric formula. At 2400 meters, the approximate atmospheric pressure can be estimated as follows:

\[ P_0 = P_{\text{sea level}} - ( \text{rate of pressure decrease} ) \times \text{altitude} \]

The rate of pressure decrease can be approximated roughly as \( 12 , \text{Pa/m} \) for average conditions. Therefore:

\[ P_0 \approx 101325 , \text{Pa} - (12 , \text{Pa/m} \times 2400 , \text{m}) = 101325 , \text{Pa} - 28800 , \text{Pa} \approx 72525 , \text{Pa} \]

Step 2: Calculate the pressure at 2.5 meters depth in water

Now we can substitute the values into the hydrostatic pressure equation:

  • \( \rho = 1000 , \text{kg/m}^3 \)
  • \( g = 9.81 , \text{m/s}^2 \)
  • \( h = 2.5 , \text{m} \)

Now, calculate the pressure due to the water:

\[ P_{\text{water}} = \rho g h = 1000 , \text{kg/m}^3 \times 9.81 , \text{m/s}^2 \times 2.5 , \text{m} = 24525 , \text{Pa} \]

Step 3: Compute the total pressure

Now, we can calculate the total pressure at this depth:

\[ P = P_0 + P_{\text{water}} = 72525 , \text{Pa} + 24525 , \text{Pa} = 97050 , \text{Pa} \]

Therefore, the local pressure at 2.5 meters depth in the swimming pool is:

\[ \boxed{97050 , \text{Pa}} \]