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An airplane is flying in a horizontal circle at a speed of \(480 \mathrm{~km} / \mathrm{h}\) (Fig. 6-41). If its wings are tilted at angle \(\theta=40^{\circ}\) to the horizontal, what is the radius of the circle in which the plane is flying? Assume that the required force is provided entirely by an "aerodynamic lift" that is perpendicular to the wing surface.

Short Answer

Expert verified
The radius of the circle is approximately 2187 meters.

Step by step solution

01

Convert Speed to Appropriate Units

First, let's convert the airplane's speed from kilometers per hour to meters per second, which is more suitable for calculations involving physics formulas:\[480 \text{ km/h} \times \frac{1000 \text{ m/km}}{3600 \text{ s/h}} = 133.33 \text{ m/s}\]
02

Understand the Forces Involved

The airplane is flying in a circle due to the 'aerodynamic lift' force, which acts perpendicular to the wings. The component of this force that acts towards the center of the circle provides the necessary centripetal force.
03

Write the Equation for Centripetal Force

The centripetal force (F_c) required is given by:\[F_c = \frac{mv^2}{r}\]where \(m\)is mass, \(v\)is velocity, and \(r\)is radius.
04

Express the Lift Force

The lift force (L) can be broken into two components: one vertical and one horizontal. The horizontal component provides the centripetal force needed for circular motion.\[L \sin \theta = \frac{mv^2}{r}\]
05

Relate Lift to Weight

We know that the vertical component of the lift force balances the weight of the airplane, \(mg\):\[L \cos \theta = mg\]
06

Solve for Lift Force (L)

Using the equation for lift balancing weight:\[L = \frac{mg}{\cos \theta}\]
07

Substitute L into Centripetal Force Equation

Substitute \(L\) in the centripetal force equation:\[\frac{mg \sin \theta}{\cos \theta} = \frac{mv^2}{r}\]
08

Simplify and Solve for Radius (r)

Cancel \(m\) from both sides and solve for \(r\):\[r = \frac{v^2}{g \tan \theta}\]Substitute in the known values (\(v = 133.33 \text{ m/s}\), \(g = 9.81 \text{ m/s}^2\), and \(\theta = 40^\circ\):\[r = \frac{(133.33)^2}{9.81 \times \tan 40^"]\]Calculate the value of \(r\).
09

Calculate the radius

Perform the calculation to find \(r\):\[r = \frac{17777.7}{9.81 \times 0.839}\approx 2187 \text{ m}\]

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Key Concepts

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

Aerodynamic Lift
Aerodynamic lift is a critical concept in understanding how airplanes are able to fly and maneuver through air. It is the force that acts perpendicular to the wing surfaces of an aircraft, allowing it to oppose the gravitational pull and maintain altitude.
The angle of the wings relative to the horizontal plays a significant role in producing lift. When an airplane tilts its wings, it affects the magnitude and direction of the aerodynamic lift force.
In the scenario described, the wings are tilted at an angle of \(40^{\circ}\), which means the lift force can be decomposed into two components:
  • Vertical Component: Balances the weight (gravity) of the airplane.
  • Horizontal Component: Provides the centripetal force necessary for circular motion.
Understanding these components helps in solving physics problems involving airplanes performing maneuvers like flying in circles. By calculating the necessary lift, one can ensure that the airplane remains stable and in continued circular motion.
Circular Motion
Circular motion involves any object moving in a curved path due to the presence of a centripetal force pointing towards the center of the circle. This force is vital to maintain the motion along the circular path.
In the airplane scenario, the centripetal force is derived from the horizontal component of the aerodynamic lift. The equation that represents this relationship is:
  • \( F_c = \frac{mv^2}{r} \)
Where \( v \) is the velocity, \( m \) is the mass, and \( r \) is the radius of the circle.
To solve for \( r \), or the radius, we incorporated both the lift force components and gravity, ensuring that the airplane has the correct centripetal force to stay in circular motion. The calculation aligns with how both the lift and gravity interact to produce the needed horizontal force.
Physics Problem Solving
Physics problem-solving involves breaking down complex problems into simpler parts that can be solved sequentially. This method is essential for understanding and resolving scenarios involving forces and motion.
In this exercise, we started by converting units for consistency, then identified all forces acting on the airplane. We used known physics principles, such as balancing forces and decomposing vectors, to express unknowns in terms of known quantities.
Steps involved were:
  • Identify the forces acting on the object.
  • Decompose forces into components.
  • Apply relevant physics equations, like those for centripetal force or balance of forces.
  • Solve the equations for the desired unknowns, such as the radius of motion.
This systematic approach is not only necessary for airplane circling problems but is also applicable to a variety of physics problems stemming from different contexts. Through consistent application, students can enhance their understanding and predictive ability regarding physical systems.

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Most popular questions from this chapter

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