/*! 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 14 A blimp is initially at rest, ho... [FREE SOLUTION] | 91Ó°ÊÓ

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A blimp is initially at rest, hovering, when at \(t=0\) the pilot turns on the motor of the propeller. The motor cannot instantly get the propeller going, but the propeller speeds up steadily. The steadily increasing force between the air and the propeller is given by the equation \(F=k t\), where \(k\) is a constant. If the mass of the blimp is \(m\), find its position as a function of time. (Assume that during the period of time you're dealing with, the blimp is not yet moving fast enough to cause a significant backward force due to air resistance.)(answer check available at lightandmatter.com)

Short Answer

Expert verified
The position of the blimp as a function of time is \( x(t) = \frac{k}{m} \frac{t^3}{6} \).

Step by step solution

01

Understanding the Problem

We need to find the position of a blimp as a function of time when the force exerted on it increases steadily with time, given by the equation \( F = k t \). The force is exerted by a propeller on the blimp, and we are told to neglect air resistance for this motion.
02

Applying Newton's Second Law

Newton's second law states that \( F = ma \), where \( F \) is the force acting on an object, \( m \) is its mass, and \( a \) is its acceleration. In this problem, the force \( F \) is given as \( k t \). Therefore, \( ma = k t \), which gives us the relation for acceleration: \( a = \frac{k}{m} t \).
03

Finding the Acceleration Function

From Step 2, we have \( a = \frac{k}{m} t \). Acceleration, \( a \), is the derivative of velocity \( v \) with respect to time \( t \): \( a = \frac{dv}{dt} = \frac{k}{m} t \).
04

Integrating to Find Velocity

To find velocity as a function of time, integrate the acceleration function: \( v(t) = \int a \, dt = \int \frac{k}{m} t \, dt = \frac{k}{m} \frac{t^2}{2} + C_v \). Since the blimp starts from rest, its initial velocity at \( t = 0 \) is 0, so \( C_v = 0 \). Thus, \( v(t) = \frac{k}{m} \frac{t^2}{2} \).
05

Integrating to Find Position

Velocity is the derivative of position \( x \) with respect to time \( t \): \( v = \frac{dx}{dt} = \frac{k}{m} \frac{t^2}{2} \). Integrating this gives the position function: \( x(t) = \int v(t) \, dt = \int \left( \frac{k}{m} \frac{t^2}{2} \right) \, dt = \frac{k}{m} \frac{t^3}{6} + C_x \). Given that the blimp starts at rest with an initial position of 0 at \( t=0 \), thus \( C_x = 0 \). Therefore, \( x(t) = \frac{k}{m} \frac{t^3}{6} \).

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Key Concepts

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

Newton's Second Law
Newton's Second Law is a fundamental principle in physics that explains the relationship between the force applied to an object, its mass, and the resulting acceleration. This law is succinctly described by the formula \( F = ma \), where \( F \) is the force acting on an object, \( m \) is the mass of the object, and \( a \) is the acceleration produced. This means that the acceleration of an object is directly proportional to the net force acting upon it and inversely proportional to its mass.
In the context of the blimp problem, the given force is expressed as a time-dependent function \( F = kt \). Integrating this with the concept of Newton's Second Law means setting \( ma = kt \), which translates into \( a = \frac{k}{m} t \). This derived formula helps us understand how acceleration changes over time given a steadily increasing force.
Understanding Newton's Second Law is crucial because it allows us to predict how an object will move when subjected to various forces, making it a cornerstone concept in understanding how dynamics of force affect motion.
Integration in Physics
Integration plays a key role in solving physics problems, especially when determining parameters like velocity and position from acceleration. In physics, acceleration is often given as a function of time, and to find the velocity, we integrate the acceleration over time. Similarly, to find position, we integrate the velocity over time.
In the case of the blimp, we begin with the acceleration function \( a = \frac{k}{m} t \). By integrating this function, we determine the velocity \( v(t) = \int a \, dt = \frac{k}{m} \frac{t^2}{2} \). The constants of integration are evaluated based on initial conditions, such as knowing the blimp started from rest, which simplifies to 0 the constant of integration for velocity.
Continuing with the process, integrating the velocity function gives us the position: \( x(t) = \int v(t) \, dt = \frac{k}{m} \frac{t^3}{6} \). Integration helps to transition between different motion parameters, allowing us to fully map out the motion of an object over time from known conditions.
Dynamics of Force
The dynamics of force describe how forces interact with masses and result in motion. In many real-world situations, forces can vary with time, just like with the blimp where the propeller force increases steadily as \( F = kt \). This example introduces the concept of time-dependent forces, which can be more complex than constant forces as they require calculus to solve for acceleration, velocity, and position.
Understanding these dynamics allows us to comprehend how velocity and position change under non-uniform forces. In physics problems like this, it's essential to account for the changing force over time, as it directly influences the resultant motion of the object.
By solving this problem, we gain insight into practical applications, such as how the increase in force over time dictates the acceleration of the blimp, eventually determining its velocity and position. Appreciating these dynamics can help further understand not just theoretical problems but also real-life scenarios where forces aren’t constant, like in cars accelerating, rockets launching, or, as we see here, a blimp starting to move.

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Most popular questions from this chapter

A person on a bicycle is to coast down a ramp of height \(h\) and then pass through a circular loop of radius \(r\). What is the smallest value of \(h\) for which the cyclist will complete the loop without falling? (Ignore the kinetic energy of the spinning wheels.)(answer check available at lightandmatter.com)

When you stand still, there are two forces acting on you, the force of gravity (your weight) and the normal force of the floor pushing up on your feet. Are these forces equal and opposite? Does Newton's third law relate them to each other? Explain.

(a) We observe that the amplitude of a certain free oscillation decreases from \(A_{0}\) to \(A_{0} / Z\) after \(n\) oscillations. Find its \(Q\). (answer check available at lightandmatter.com) (b) The figure is from Shape memory in Spider draglines, Emile, Le Floch, and Vollrath, Nature 440:621 (2006). Panel 1 shows an electron microscope's image of a thread of spider silk. In 2, a spider is hanging from such a thread. From an evolutionary point of view, it's probably a bad thing for the spider if it twists back and forth while hanging like this. (We're referring to a back-and- forth rotation about the axis of the thread, not a swinging motion like a pendulum.) The authors speculate that such a vibration could make the spider easier for predators to see, and it also seems to me that it would be a bad thing just because the spider wouldn't be able to control its orientation and do what it was trying to do. Panel 3 shows a graph of such an oscillation, which the authors measured using a video camera and a computer, with a \(0.1 \mathrm{~g}\) mass hung from it in place of a spider. Compared to human-made fibers such as kevlar or copper wire, the spider thread has an unusual set of properties: 1\. It has a low \(Q\), so the vibrations damp out quickly. 2\. It doesn't become brittle with repeated twisting as a copper wire would. 3\. When twisted, it tends to settle in to a new equilibrium angle, rather than insisting on returning to its original angle. You can see this in panel 2, because although the experimenters initially twisted the wire by 35 degrees, the thread only performed oscillations with an amplitude much smaller than \(\pm 35\) degrees, settling down to a new equilibrium at 27 degrees. 4\. Over much longer time scales (hours), the thread eventually resets itself to its original equilbrium angle (shown as zero degrees on the graph). (The graph reproduced here only shows the motion over a much shorter time scale.) Some humanmade materials have this "memory" property as well, but they typically need to be heated in order to make them go back to their original shapes. Focusing on property number 1 , estimate the \(Q\) of spider silk from the graph.(answer check available at lightandmatter.com)

At the 2010 Salinas Lettuce Festival Parade, the Lettuce Queen drops her bouquet while riding on a float moving toward the right. Sketch the shape of its trajectory in her frame of reference, and compare with the shape seen by one of her admirers standing on the sidewalk.

A baseball pitcher throws a pitch clocked at \(v_{x}=73.3 \mathrm{mi} / \mathrm{h}\). He throws horizontally. By what amount, \(d\), does the ball drop by the time it reaches home plate, \(L=60.0 \mathrm{ft}\) away? (a) First find a symbolic answer in terms of \(L, v_{x}\), and \(g\). (answer check available at lightandmatter.com) (b) Plug in and find a numerical answer. Express your answer in units of ft. (Note: \(1 \mathrm{ft}=12\) in, \(1 \mathrm{mi}=5280 \mathrm{ft}\), and \(1 \mathrm{in}=2.54 \mathrm{~cm}\) ) (answer check available at lightandmatter.com)

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