Ch 05: Force and Motion

Knight Calc - Physics for Scientists and Engineers 5th Edition

Knight Calc5th EditionPhysics for Scientists and EngineersISBN: 9780137344796Not the one you use?Change textbook

Knight Calc 5th Edition

Ch 05: Force and Motion

Problem 5a

Chapter 5, Problem 5a

A jet plane is speeding down the runway during takeoff. Air resistance is not negligible. Identify the forces on the jet.

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Identify the gravitational force acting on the jet: The weight of the jet, \( F_g = m \cdot g \), acts downward toward the center of the Earth, where \( m \) is the mass of the jet and \( g \) is the acceleration due to gravity (approximately \( 9.8 \, \text{m/s}^2 \)).

Identify the normal force: The ground exerts an upward normal force \( F_N \) on the jet, which counteracts the downward gravitational force. This force is perpendicular to the surface of the runway.

Identify the thrust force: The engines of the jet produce a forward thrust force \( F_{\text{thrust}} \), which propels the jet forward along the runway.

Identify the air resistance: Air resistance, or drag force \( F_{\text{drag}} \), acts opposite to the direction of motion of the jet. This force depends on factors such as the speed of the jet, its shape, and the density of the air.

Summarize the forces: The forces acting on the jet are the gravitational force \( F_g \), the normal force \( F_N \), the thrust force \( F_{\text{thrust}} \), and the air resistance \( F_{\text{drag}} \). These forces combine to determine the net force and acceleration of the jet during takeoff.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Forces Acting on an Object

In physics, forces are interactions that can change the motion of an object. When analyzing a jet plane during takeoff, we consider both the forces acting on it and their directions. The primary forces include thrust from the engines, drag due to air resistance, lift generated by the wings, and weight due to gravity.

Thrust

Thrust is the force that propels an aircraft forward, generated by its engines. In the context of a jet plane, thrust must overcome both drag and weight for the plane to accelerate down the runway and achieve takeoff speed. It is crucial for understanding how the plane gains speed and altitude.

Drag

Drag is the aerodynamic resistance that opposes an aircraft's motion through the air. It increases with the speed of the jet and is influenced by factors such as the shape of the aircraft and air density. Understanding drag is essential for analyzing the forces acting on the jet during takeoff, as it affects the required thrust and overall performance.

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