/*! 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 37 Multiple-Concept Example 10 offe... [FREE SOLUTION] | 91Ó°ÊÓ

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Multiple-Concept Example 10 offers useful background for problems like this. A cylinder is rotating about an axis that passes through the center of each circular end piece. The cylinder has a radius of \(0.0830 \mathrm{m},\) an angular speed of 76.0 \(\mathrm{rad} / \mathrm{s}\) , and a moment of inertia of 0.615 \(\mathrm{kg} \cdot \mathrm{m}^{2}\) . A brake shoe presses against the surface of the cylinder and applies a tangential frictional force to it. The frictional force reduces the angular speed of the cylinder by a factor of two during a time of 6.40 s. \((\text { a) Find the magnitude of the angular deceleration of the }\) cylinder. (b) Find the magnitude of the force of friction applied by the brake shoe.

Short Answer

Expert verified
(a) Angular deceleration is -5.94 rad/s². (b) Frictional force is 44.1 N.

Step by step solution

01

Find Initial and Final Angular Speed

The initial angular speed \( \omega_0 \) is given as 76.0 rad/s. The problem states that the angular speed is reduced by a factor of two, so the final angular speed \( \omega \) after 6.40 s is:\[ \omega = \frac{\omega_0}{2} = \frac{76.0}{2} = 38.0 \text{ rad/s} \]
02

Calculate Angular Deceleration

The angular deceleration \( \alpha \) can be found using the equation:\[ \alpha = \frac{\omega - \omega_0}{t} \]Substitute the known values:\[ \alpha = \frac{38.0 \text{ rad/s} - 76.0 \text{ rad/s}}{6.40 \text{ s}} = \frac{-38.0}{6.40} \]\[ \alpha = -5.94 \text{ rad/s}^2 \]The negative sign indicates deceleration.
03

Calculate Torque due to Friction

Using the relationship between torque \( \tau \), moment of inertia \( I \), and angular acceleration \( \alpha \):\[ \tau = I \cdot \alpha \]Substitute the known values:\[ \tau = 0.615 \text{ kg} \cdot \text{m}^2 \times (-5.94 \text{ rad/s}^2) \]\[ \tau = -3.66 \text{ N} \cdot \text{m} \]
04

Calculate Frictional Force

Torque is also related to the radius and frictional force \( F_f \) by:\[ \tau = r \cdot F_f \]Where \( r = 0.0830 \text{ m} \). Solve for \( F_f \):\[ F_f = \frac{\tau}{r} = \frac{3.66 \text{ N} \cdot \text{m}}{0.0830 \text{ m}} = 44.1 \text{ N} \]

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Key Concepts

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

Angular Deceleration
Angular deceleration refers to the rate at which the angular speed of an object decreases over time. When an object like a rotating cylinder slows down, this is due in part to angular deceleration. It is important to note that angular deceleration is simply the opposite of angular acceleration and can be calculated using a similar formula. In the case of the above problem, it is given by:\[ \alpha = \frac{\omega - \omega_0}{t} \]where \( \omega_0 \) is the initial angular speed, \( \omega \) is the final angular speed, and \( t \) is the time over which the change occurs.- Angular deceleration is often expressed in radians per second squared \( \text{rad/s}^2 \).- The negative sign in angular deceleration indicates a reduction in angular speed, or slowing down of the rotation.
Understanding angular deceleration is crucial in many practical applications, such as braking systems in vehicles and controlling the speed of turbines in windmills.
Moment of Inertia
Moment of inertia is a measure of an object's resistance to changes in its rotational motion. It depends on both the mass of the object and how that mass is distributed relative to the axis of rotation.- For a solid cylinder, the moment of inertia is given by: \[ I = \frac{1}{2}mR^2 \] where \( m \) is the mass and \( R \) is the radius of the cylinder.The higher the moment of inertia, the more difficult it is to change the rotational speed of the object. This property can be compared to mass in linear motion; just as a heavier object is harder to accelerate or decelerate in a straight line, an object with a larger moment of inertia is harder to spin faster or slow down.- Moment of inertia is a pivotal concept in designing gears, flywheels, and other rotational systems.
Knowing this helps engineers control how fast or slow objects should be able to rotate.
Angular Speed
Angular speed is the rate at which an object rotates or revolves around an axis and is expressed in radians per second \( \text{rad/s} \). Angular speed provides a measure of how quickly an object can complete a rotation. In the exercise, the initial angular speed is given as 76 rad/s, which then gets reduced by a braking system.- Calculating angular speed involves finding out how many radians an object covers in a given unit of time.- It can be pivotal for understanding and comparing the speeds of rotating systems, like wheels or fans.- Angular speed is an essential concept in fields such as mechanical engineering and astrophysics.
In practical applications, knowing the angular speed helps in designing efficient rotational systems, monitoring equipment operations, and predicting the overall behavior of spinning objects.
Frictional Force
Frictional force is the resisting force encountered by an object in motion, and when applied to rotational motion, it slows down or stops the rotational movement. In the given problem, a brake shoe applies a tangential frictional force to the cylinder.- The force of friction can be calculated using the torque caused by the friction and is related to the radius of the rotating object: \[ \tau = r \cdot F_f \] where \( \tau \) is the torque, \( r \) is the radius, and \( F_f \) is the frictional force.This frictional force plays a crucial role in braking systems, helping control the motion of vehicles and machinery. Factors affecting frictional force include the surface texture and material in contact with the rotating object.- Understanding frictional force is crucial for ensuring safety and efficiency in mechanical systems.
Designing effective braking systems or managing wear in rotating machinery are practical applications that rely on a detailed understanding of how friction affects rotational motion.

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Most popular questions from this chapter

A clay vase on a potter's wheel experiences an angular acceleration of 8.00 \(\mathrm{rad} / \mathrm{s}^{2}\) due to the application of a \(10.0-\mathrm{N} \cdot \mathrm{m}\) net torque. Find the total moment of inertia of the vase and potter's wheel.

In outer space two identical space modules are joined together by a massless cable. These modules are rotating about their center of mass, which is at the center of the cable because the modules are identical (see the drawing). In each module, the cable is connected to a motor, so that the modules can pull each other together. The initial tangential speed of each module is \(v_{0}=17 \mathrm{m} / \mathrm{s}\) . Then they pull together until the distance between them is reduced by a factor of two. Each module has a final tangential speed of \(v_{\mathrm{f}}\) . Find the value of \(v_{\mathrm{f}}\)

One end of a thin rod is attached to a pivot, about which it can rotate without friction. Air resistance is absent. The rod has a length of 0.80 m and is uniform. It is hanging vertically straight downward. The end of the rod nearest the floor is given a linear speed \(v_{0},\) so that the rod begins to rotate upward about the pivot. What must be the value of \(v_{0}\) . such that the rod comes to a momentary halt in a straight-up orientation, exactly opposite to its initial orientation?

A cylindrically shaped space station is rotating about the axis of the cylinder to create artificial gravity. The radius of the cylinder is 82.5 m. The moment of inertia of the station without people is \(3.00 \times 10^{9} \mathrm{kg} \cdot \mathrm{m}^{2}\) . Suppose that 500 people, with an average mass of 70.0 \(\mathrm{kg}\) each, live on this station. As they move radially from the outer surface of the cylinder toward the axis, the angular speed of the station changes. What is the maximum possible percentage change in the station's angular speed due to the radial movement of the people?

Consult Multiple-Concept Example 10 to review an approach to problems such as this. A CD has a mass of 17 g and a radius of 6.0 cm. When inserted into a player, the CD starts from rest and accelerates to an angular velocity of 21 rad/s in 0.80 s. Assuming the CD is a uniform solid disk, determine the net torque acting on it.

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