/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 50 Loss of power! In December of \(... [FREE SOLUTION] | 91Ó°ÊÓ

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Loss of power! In December of \(1989,\) a KLM Boeing 747 airplane carrying 231 passengers entered a cloud of ejecta from an Alaskan volcanic eruption. All four engines went out, and the plane fell from \(27,900\) ft to \(13,300\) ft before the engines could be restarted. It then landed safely in Anchorage. Neglecting any air resistance and aerodynamic lift, and assuming that the plane had no vertical motion when it lost power, (a) for how long did it fall before the engines were restarted, and (b) how fast was it falling at that instant? c) In reality, why would the plane not be falling nearly as fast?

Short Answer

Expert verified
(a) The plane fell for about 30.1 seconds. (b) It was falling at approximately 969.22 ft/s when the engines were restarted. (c) In reality, factors like aerodynamic lift and air resistance reduce falling speed.

Step by step solution

01

Identify Known Quantities

We know the initial height (\(h_i = 27,900 \text{ ft}\)) and the final height (\(h_f = 13,300 \text{ ft}\)). The acceleration due to gravity is \(g = 32.2 \text{ ft/s}^2\), and the initial vertical velocity is \(v_i = 0 \text{ ft/s}\) since the plane had no vertical motion when it lost power.
02

Calculate Height Difference

Calculate the difference in height that the plane fell: \(\Delta h = h_i - h_f = 27,900 \text{ ft} - 13,300 \text{ ft} = 14,600 \text{ ft}\). This is the distance the plane fell.
03

Use Kinematic Equation to Find Time

The formula for the distance fallen under constant acceleration with initial velocity zero is \(\Delta h = \frac{1}{2} g t^2\). Solve for \(t\): \[ 14,600 = \frac{1}{2} \times 32.2 \times t^2 \]This gives: \[ t^2 = \frac{14,600 \times 2}{32.2} \approx 906.21 \]\[ t \approx \sqrt{906.21} \approx 30.10 \text{ seconds} \] The plane fell for approximately 30.1 seconds.
04

Use Kinematic Equation to Find Final Velocity

Use the formula \(v_f = v_i + g t\) to find final velocity:\[ v_f = 0 + 32.2 \times 30.10 \]\[ v_f \approx 32.2 \times 30.10 \approx 969.22 \text{ ft/s} \] The plane was descending at approximately 969.22 ft/s when the engines restarted.
05

Discuss Real-life Factors

In reality, factors like aerodynamic lift and air resistance would significantly slow the descent of the plane, resulting in a slower falling speed and a different time duration compared to ideal conditions.

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Key Concepts

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

Kinematic Equations
Kinematic equations are fundamental in physics, particularly in mechanics, to describe the motion of objects. These equations can predict an object's future motion when we know its current state. The main kinematic equations are:
  • \( v = u + at \): Final velocity \( v \) after time \( t \), with initial velocity \( u \) and acceleration \( a \).
  • \( s = ut + \frac{1}{2} a t^2 \): Displacement \( s \) after time \( t \).
  • \( v^2 = u^2 + 2as \): Links velocity to displacement.
In the exercise, these equations help us calculate how long the plane falls and the speed it reaches. By knowing initial conditions and assuming constant acceleration (due to gravity), we use \( \Delta h = \frac{1}{2} g t^2 \) to find the time and \( v_f = v_i + g t \) for speed. This approach assumes no air resistance and is key to solving many physics problems.
Acceleration due to Gravity
Acceleration due to gravity is a crucial concept in understanding how objects fall freely towards Earth. It is primarily due to Earth's gravitational pull.On Earth, the standard acceleration due to gravity is approximately \(9.81 \text{ m/s}^2\) or \(32.2 \text{ ft/s}^2\) in the imperial unit system. This constant force acts downwards towards the Earth's center and affects all objects equally, regardless of their mass.In our plane exercise, the acceleration due to gravity is used to determine both the falling time and the velocity. This exercise highlights how gravity impacts motion, especially when other forces like air resistance are neglected.Keep in mind that in reality, this value can slightly change due to height above sea level or local mass differences in Earth's crust.
Vertical Velocity
Vertical velocity is the speed at which an object moves up or down. In the context of free fall, it is controlled by gravity if no other forces act on the object.At the start of the fall, our plane's vertical velocity was zero because it wasn't moving up or down. However, under gravity's influence, its vertical velocity increased continuously until the engines restarted.Using the kinematic equation \( v_f = v_i + g t \), the final vertical velocity is found. This tells us how rapid the object's descent becomes over time. In the exercise, the final velocity calculated was about \(969.22 \text{ ft/s}\), showcasing significant descent speed. Understanding how velocity changes over time is vital in predicting an object's future state.
Aerodynamic Lift
Aerodynamic lift is a force that opposes gravity and enables aircraft to remain in the air. It originates from differences in air pressure on different sides of an airfoil (like a wing) due to its shape and motion. Lift is primarily generated due to Bernoulli’s principle, which explains that an increase in the fluid's speed leads to a decrease in pressure. The plane's wings are designed so air moves faster over them than underneath, creating a lift that counteracts gravity. In the exercise, the absence of aerodynamic lift and air resistance significantly impacted the free fall rate. In reality, with engines off, remaining aerodynamic lift would reduce the speed of descent considerably, providing a more stable and slower fall than calculated."

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