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The Milkin Aircraft Co. manufactures a turbojet cngine that is placed in a plane having a weight of \(130001 b\). If the engine develops a constant thrust of 5200 lb, determine the power output of the plane when it is just ready to take off with a speed of \(600 \mathrm{mi} / \mathrm{h}\)

Short Answer

Expert verified
The power output of the plane just before takeoff is 4,576,000 foot-pounds per second.

Step by step solution

01

Understand the Variables Given

Identify and understand the variables provided. The thrust of the engine, which is the force the plane uses to move is given as 5200 lb. The velocity or speed of the plane just before it takes off is also given as 600 miles per hour.
02

Convert the Speed to fps

Before proceeding with the calculations, convert the speed of the plane from miles per hour to feet per second because power is typically calculated in foot-pounds per second. There are 5280 feet in a mile and 3600 seconds in an hour. So, \( 600 \, mi/h = 600 \times \frac{5280}{3600} = 880 \, ft/s \)
03

Calculate Power Output

Use the formula for power which is \( power = force \times velocity \). The force is equal to the thrust of the engine, and the velocity is the speed of the plane. So, \( power = 5200 \, lb \times 880 \, ft/s = 4,576,000 \, ft \cdot lb/s \)

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Key Concepts

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

Turbojet Engine Thrust
Understanding the power of a turbojet engine begins with comprehending the concept of thrust. Thrust is the force generated by the engine to propel the aircraft forward through the air. It is the result of the aircraft’s propulsion system expelling mass in one direction and thereby generating an equal and opposite reaction force, in accordance with Newton's third law of motion.

In our context, the Milkin Aircraft Company’s engine generates a thrust of 5200 pounds (lb). This value is crucial as it directly affects the acceleration and eventual velocity the aircraft will achieve. The engine's thrust capability serves as a determining factor for various performance measures, such as take-off speed, climb rate, and maximum speed.

When calculating power output, this thrust force, when multiplied by the aircraft's velocity at the moment of takeoff, gives us a measure of how much work the engine can do over a certain period. In simpler terms, the higher the thrust produced by a turbojet engine, the greater potential for work and thus higher power output.
Force and Velocity Relationship
The relationship between force and velocity is central to understanding mechanical power. Power, in the context of physics, is defined as the rate at which work is done. It is quantified by the amount of work completed in a given amount of time. When we talk about force in this scenario, we are referring to the thrust exerted by the jet engine, and velocity is the speed at which the aircraft moves.

In terms of an equation, power (P) can be calculated by the product of force (F) and velocity (v), that is,
\[ P = F \times v \]
When thrust (a type of force) is constant and acting in the direction of the velocity, calculating power output becomes straightforward. It is essential, however, to ensure that both quantities are expressed in compatible units before performing the multiplication. The result will give you the instantaneous power output at the moment of the aircraft's takeoff, providing insight into the engine's performance at that specific condition.
Unit Conversion
In physics and engineering, precise calculations often demand that units are converted to align with the standard unit systems used. For solving the given problem, it’s important to convert the velocity of the plane from miles per hour to feet per second, aligning it with the thrust given in pounds.

To convert velocity for our purpose:
  • The standard conversion factor between miles and feet is 5280 feet = 1 mile.
  • Time is similarly converted between hours and seconds with the fact that 3600 seconds = 1 hour.
Using these conversions, the speed of the plane at takeoff can be translated to:
\[ 600 \text{ mi/h} = 600 \times \frac{5280 \text{ ft}}{3600 \text{ s}} = 880 \text{ ft/s} \]
These types of unit conversions are fundamental to ensuring consistency and accuracy in calculations, allowing us to compute the power output correctly. Being proficient in unit conversion is a key skill in fields such as physics, engineering, and applied sciences, and it’s critical for solving many real-world problems.

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Most popular questions from this chapter

The car \(C\) and its contents have a weight of \(6001 b\) whereas block \(B\) has a weight of 200 lb. If the car is released from rest, determine its speed when it travels \(30 \mathrm{ft}\) down the \(20^{\circ}\) incline. Suggestion: To measure the gravitational potential energy, establish separate datums at the initial elevations of \(B\) and \(C\)

The block has a mass of \(150 \mathrm{kg}\) and rests on a surface for which the coefficients of static and kinetic friction are \(\mu_{s}=0.5\) and \(\mu_{k}=0.4,\) respectively. If a force \(F=\left(60 t^{2}\right) \mathrm{N},\) where \(t\) is in seconds, is applied to the cable, determine the power developed by the force when \(t=5\) s. Hint: First determine the time needed for the force to cause motion.

The block has a weight of \(80 \mathrm{lb}\) and rests on the floor for which \(\mu_{k}=0.4 .\) If the motor draws in the cable at a constant rate of \(6 \mathrm{ft} / \mathrm{s}\), determine the output of the motor at the instant \(\theta=30^{\circ} .\) Neglect the mass of the cable and pulleys.

A rocket of mass \(m\) is fired vertically from the surface of the earth, i.e., at \(r=r_{1} .\) Assuming that no mass is lost as it travels upward, determine the work it must do against gravity to reach a distance \(r_{2} .\) The force of gravity is \(F=G M_{e} m / r^{2}\) (Eq. \(13-1\) ), where \(M_{e}\) is the mass of the carth and \(r\) the distance between the rocket and the center of the earth.

The 50 -lb crate is given a speed of \(10 \mathrm{ft} / \mathrm{s}\) in \(t=4 \mathrm{s}\) starting from rest. If the acceleration is constant, determine the power that must be supplied to the motor when \(t=2\) s. The motor has an efficiency \(\varepsilon=0.65 .\) Neglect the mass of the pulley and cable.

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