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Grade upto college level Mechanics

A Pitot tube is mounted on an airplane wing to determine the speed of the plane relative to the air, which has a density of 1.03 kg/m3. The tube contains alcohol and indicates a level difference of 26.2 cm. What is the plane's speed relative to the air? The density of alcohol is 810 kg/m3.

Profile image of Amit Saxena
11 Years agoGrade upto college level
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1 Answer

Profile image of Navjyot Kalra
11 Years ago

To find the speed of the airplane relative to the air using the Pitot tube information you provided, we can use Bernoulli’s principle and the concept of pressure difference. The Pitot tube measures the dynamic pressure caused by the airplane's speed, which can then be related to the airspeed. Let's break this down step by step.

Understanding the Fundamentals

A Pitot tube measures the difference between the static pressure of the air and the total pressure (dynamic plus static) as the aircraft moves through the air. This difference in pressure is what allows us to calculate the airspeed. The formula we will use is derived from Bernoulli's equation and is given as:

Formula for Airspeed

The speed (V) of the airplane can be calculated using the equation:

V = √(2 * ΔP / ρ)

  • ΔP is the pressure difference measured by the Pitot tube.
  • ρ is the density of the fluid (in this case, air).

Calculating the Pressure Difference

The pressure difference (ΔP) can be calculated from the height difference indicated by the alcohol in the Pitot tube. Since the density of the alcohol is given as 810 kg/m³, we can use the hydrostatic pressure formula:

ΔP = h * ρ * g

Where:

  • h is the height difference (26.2 cm or 0.262 m).
  • ρ is the density of the alcohol (810 kg/m³).
  • g is the acceleration due to gravity (approximately 9.81 m/s²).

Substituting Values

Now, we can plug in the values to find ΔP:

ΔP = 0.262 m * 810 kg/m³ * 9.81 m/s²

Calculating this gives:

ΔP ≈ 0.262 * 810 * 9.81 ≈ 2071.12 Pa

Finding the Airspeed

Now that we have the pressure difference, we can substitute this back into the airspeed equation:

V = √(2 * 2071.12 Pa / 1.03 kg/m³)

Calculating this gives:

V = √(2 * 2071.12 / 1.03)

V ≈ √(4025.55) ≈ 63.41 m/s

Final Answer

Thus, the speed of the airplane relative to the air is approximately 63.41 meters per second. This value provides a clear understanding of how the Pitot tube functions in determining the aircraft's airspeed by leveraging principles of fluid dynamics.