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You are designing a diving bell to withstand the pressure of seawater at a depth of 250 \(\mathrm{m}\) . (a) What is the gauge pressure at this depth? (You can ignore changes in the density of the water with depth. \((\mathrm{b})\) At this depth, what is the net force due to the water outside and the air inside the bell on a circular glass window 30.0 \(\mathrm{cm}\) in diameter if the pressure inside the diving bell equals the pressure at the surface of the water? (You can ignore the small variation of pressure over the surface of the window.)

Short Answer

Expert verified
(a) Gauge pressure at 250 m is 2,512,250 Pa; (b) The net force on the window is 170,459 N.

Step by step solution

01

Define given values for gauge pressure calculation

We are given the depth at which the diving bell operates: 250 m. We will use the density of seawater, which is approximately 1025 kg/m³, and the acceleration due to gravity, 9.8 m/s², to find the gauge pressure.
02

Calculate gauge pressure at the depth

Gauge pressure can be calculated using the formula \( P = \rho g h \), where \( \rho \) is the density of seawater, \( g \) is the acceleration due to gravity, and \( h \) is the depth. So, \( P = 1025 \times 9.8 \times 250 \).
03

Compute gauge pressure numerical value

Calculate \( P = 1025 \times 9.8 \times 250 = 2,512,250 \) Pa. The gauge pressure at this depth is 2,512,250 Pa.
04

Determine diameter and radius for net force calculation

The diameter of the circular glass window is 30.0 cm, which is 0.3 meters. The radius \( r \) is half of the diameter, so \( r = 0.15 \) meters.
05

Calculate area of the glass window

The area \( A \) of the circular window is given by the formula \( A = \pi r^2 \). Substituting the radius, we have: \( A = \pi \times (0.15)^2 \).
06

Compute the area of the window

Calculate \( A = \pi \times 0.0225 \approx 0.0707 \) m².
07

Understand pressure conditions for net force

The pressure inside the bell is equal to atmospheric pressure, around 101,325 Pa. The external gauge pressure due to seawater is 2,512,250 Pa, as calculated earlier.
08

Calculate net pressure on the window

The net pressure \( P_{\text{net}} \) acting on the window is the difference between external gauge pressure and internal atmospheric pressure: \( P_{\text{net}} = 2,512,250 - 101,325 = 2,410,925 \) Pa.
09

Compute the net force on the glass window

The net force \( F \) can be calculated using \( F = P_{\text{net}} \times A \). Substituting the values: \( F = 2,410,925 \times 0.0707 \).
10

Calculate the numerical value of net force

Calculate \( F = 170,459.07 \) N. The net force acting on the window is approximately 170,459.07 N.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Net Force Calculation
When it comes to studying forces, understanding how to compute net force is critical. Here, we are concerned with how the forces at play affect the circular window of a diving bell. The diving bell is submerged under the sea at a depth of 250 meters. At this depth, the water exerts a significant external pressure on the window of the bell. This pressure is different from the atmospheric pressure inside the bell, which remains at surface levels.To find the net force, start by determining the net pressure. Net pressure is essentially the difference between the pressure exerted by seawater at this depth and the atmospheric pressure inside the bell:\[ P_{\text{net}} = P_{\text{external}} - P_{\text{internal}} \]Since the pressure inside the bell is equal to atmospheric pressure and the pressure outside is much greater, the net pressure translates into a force pushing inward. With the net pressure calculated, use this to find the net force acting on the window. Compute it using the formula:\[ F = P_{\text{net}} \times A \]where \( A \) is the area of the window. This calculation helps you understand how much force the glass window has to withstand to prevent seawater from breaching the bell. This force, as found to be 170,459.07 N, implies the massive load that the window supports underwater.
Density of Seawater
A key component in the calculation of pressure under the sea is the density of seawater. This is because density affects how much pressure a specific volume of seawater exerts. For most oceanic calculations, seawater is assumed to have a density of about 1025 kg/m³.Density, denoted by \( \rho \), is crucial for any calculation of pressure at a certain depth in the ocean through the formula:\[ P = \rho g h \]where \( \rho \) is the density of seawater, \( g \) is the acceleration due to gravity (approximately 9.8 m/s²), and \( h \) is the depth in meters. This formula shows us that pressure increases proportionally to depth and density.Understanding seawater density helps when considering variations in ocean conditions. Although seawater density can be influenced by factors such as temperature and salinity, for many practical calculations like this one, a constant density simplifies the process. This constant value provides a solid basis to predict and counteract the underwater pressures faced by the diving bell.
Circular Window Area
To understand the forces at play on a diving bell's window, it's important to comprehend how to calculate the area of a circular window. The area determines how much force acts on the window for a given pressure.Begin with the window's diameter, which, in the case of the diving bell, is given as 30.0 cm or 0.3 meters. The radius, which is half of the diameter, is calculated as:\[ r = \frac{\text{diameter}}{2} = 0.15 \text{ meters} \]Using the radius, find the area \( A \) of the window using the formula for the area of a circle:\[ A = \pi r^2 \]Substituting the radius value gives:\[ A = \pi \times (0.15)^2 \approx 0.0707 \text{ m}^2 \]This area is a key component in the calculation of the net force since it scales the effect of net pressure across the entire window's surface. This highlights why it's crucial to know and apply the principles of geometry when assessing the integrity and safety of structures designed to withstand high pressures. Understanding these calculations can help ensure that the window can withstand the pressures at the depth it operates. By mastering this concept, you can design safer and more effective underwater structures.

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