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A constant horizontal force \(\vec{F}_{\text {app }}\) of magnitude \(12 \mathrm{~N}\) is applied to a uniform solid cylinder by fishing line wrapped around the cylinder. The mass of the cylinder is \(10 \mathrm{~kg}\), its radius is \(0.10 \mathrm{~m}\), and the cylinder rolls smoothly on the horizontal surface. (a) What is the magnitude of the acceleration of the center of mass of the cylinder? (b) What is the magnitude of the angular acceleration of the cylinder about the center of mass? (c) In unit-vector notation, what is the frictional force acting on the cylinder?

Short Answer

Expert verified
(a) 0.8 m/s²; (b) 8 rad/s²; (c) -4 N \(\hat{i}\).

Step by step solution

01

Define the forces acting on the cylinder

We have a horizontal applied force \( F_{\text{app}} \) of 12 N, and the cylinder is rolling smoothly. Thus, there must be a frictional force \( f \) acting at the point of contact with the ground to allow rolling without slipping.
02

Write the equation of motion for linear acceleration

Using Newton's second law, the equation for the linear motion of the center of mass is \( F_{\text{app}} - f = m a \), where \( F_{\text{app}} = 12 \text{ N} \), \( m = 10 \text{ kg} \), and \( a \) is the linear acceleration.
03

Write the equation of motion for angular acceleration

The net torque \( \tau \) about the center of mass due to the frictional force is \( \tau = fR \), where \( R = 0.10 \text{ m} \) is the radius of the cylinder. Using the moment of inertia for a solid cylinder \( I = \frac{1}{2} m R^2 \), the angular acceleration \( \alpha \) is given by \( \tau = I \alpha \).
04

Relate linear and angular acceleration for rolling motion

For rolling without slipping, the linear acceleration \( a \) is related to the angular acceleration \( \alpha \) by \( a = \alpha R \).
05

Solve the equations for acceleration

Using the equations from Steps 2, 3, and 4, we have two equations: \( F_{\text{app}} - f = ma \) and \( fR = \frac{1}{2} m R^2 \alpha \). Substitute \( \alpha = \frac{a}{R} \) into the torque equation to eliminate \( \alpha \). Then solve for \( a \).
06

Calculate the magnitude of linear acceleration

From \( F_{\text{app}} = ma + \frac{1}{2} ma \), solve for \( a \):\[ 12 = \frac{3}{2} \cdot 10 \cdot a \]\[ a = \frac{\frac{2}{3} \cdot 12}{10} = 0.8 \; \text{ms}^{-2} \]
07

Calculate the angular acceleration

Use \( \alpha = \frac{a}{R} \) and substitute \( a = 0.8 \; \text{ms}^{-2} \) and \( R = 0.1 \text{ m} \):\[ \alpha = \frac{0.8}{0.1} = 8 \; \text{rad/s}^2 \]
08

Identify the frictional force

Substitute \( a = 0.8 \; \text{ms}^{-2} \) back into \( f = ma \), where \( f = \frac{1}{2} \cdot 10 \cdot 0.8 \):\[ f = 4 \; \text{N} \] The frictional force is directed opposite to the applied force, so \( \vec{f} = -4\hat{i} \text{ N} \).

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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 how the velocity of an object changes when it's subjected to an external force. It is expressed by the equation \( F = ma \), where \( F \) is the net force acting on the object, \( m \) is the mass of the object, and \( a \) is the linear acceleration it undergoes.

In our problem scenario, the horizontal force applied to the cylinder (\( F_{\text{app}} = 12 \text{ N} \)) causes it to accelerate. The cylinder's resistance to change in motion, due to its mass \( m \) of 10 kg, combined with the frictional force, which ensures it rolls smoothly, allows us to apply Newton's Second Law. We have:- Applied force \( F_{\text{app}} \)- Frictional force \( f \)

The net force equation is formed as \( F_{\text{app}} - f = ma \). Solving this gives the linear acceleration \( a \) for the cylinder's center of mass.
Torque and Rotational Motion
In rotational motion, torque is the rotational equivalent of force. Torque produces angular acceleration in a body. The amount of torque \( \tau \) depends on the force applied and the distance from the pivot point, calculated by \( \tau = fR \), where \( R \) is the radius of the rotation path.

For our cylinder, the frictional force \( f \) creates a torque about its center of mass. The moment of inertia (\( I \)) for a solid cylinder, which represents the mass distribution relative to the axis of rotation, is given by \( I = \frac{1}{2}mR^2 \). This formula accounts for how difficult it is to change the cylinder's rotational state.
  • Torque \( \tau = fR \)
  • Moment of Inertia \( I = \frac{1}{2}mR^2 \)
Using these relations, the angular acceleration \( \alpha \) can be found using \( \tau = I \alpha \). This demonstrates how torque and moment of inertia are vital to understanding rotational motions.
Linear and Angular Acceleration
Linear and angular accelerations are closely related when dealing with rolling objects. Linear acceleration \( a \) measures how quickly the velocity of the cylinder's center of mass changes, while angular acceleration \( \alpha \) concerns how fast the cylinder's rotation speeds up.

For a rolling cylinder, without slipping, these accelerations are connected through the relationship \( a = \alpha R \), where \( R \) is the cylinder's radius. Using this bridge between linear and angular motion allows us to solve problems involving objects that roll instead of sliding:
  • Linear acceleration (\( a \)) affects the motion along a path.
  • Angular acceleration (\( \alpha \)) affects how quickly an object rotates.
By applying this relationship in our problem, and knowing the radius and the calculated linear acceleration, we determined the angular acceleration. This reflects how the cylinder's movement on the surface is governed by these interconnected accelerations.

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Most popular questions from this chapter

A yo-yo has a rotational inertia of \(950 \mathrm{~g} \cdot \mathrm{cm}^{2}\) and a mass of \(120 \mathrm{~g}\). Its axle radius is \(3.2 \mathrm{~mm}\), and its string is \(120 \mathrm{~cm}\) long. The yo-yo rolls from rest down to the end of the string. (a) What is the magnitude of its linear acceleration? (b) How long does it take to reach the end of the string? As it reaches the end of the string, what are its (c) linear speed, (d) translational kinetic energy, (e) rotational kinetic energy, and (f) angular speed?

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A uniform disk of mass \(10 m\) and radius \(3.0 r\) can rotate freely about its fixed center like a merry-go-round. A smaller uniform disk of mass \(m\) and radius \(r\) lies on top of the larger disk, concentric with it. Initially the two disks rotate together with an angular velocity of \(20 \mathrm{rad} / \mathrm{s}\). Then a slight disturbance causes the smaller disk to slide outward across the larger disk, until the outer edge of the smaller disk catches on the outer edge of the larger disk. Afterward, the two disks again rotate together (without further sliding). (a) What then is their angular velocity about the center of the larger disk? (b) What is the ratio \(K / K_{0}\) of the new kinetic energy of the two-disk system to the system's initial kinetic energy?

A sanding disk with rotational inertia \(1.2 \times 10^{-3} \mathrm{~kg} \cdot \mathrm{m}^{2}\) is attached to an electric drill whose motor delivers a torque of magnitude \(16 \mathrm{~N} \cdot \mathrm{m}\) about the central axis of the disk. About that axis and with the torque applied for \(33 \mathrm{~ms}\), what is the magnitude of the (a) angular momentum and (b) angular velocity of the disk?

Force \(\vec{F}=(2.0 \mathrm{~N}) \hat{\mathrm{i}}-(3.0 \mathrm{~N}) \hat{\mathrm{k}}\) acts on a pebble with posi- tion vector \(\vec{r}=(0.50 \mathrm{~m}) \hat{\mathrm{j}}-(2.0 \mathrm{~m}) \hat{\mathrm{k}}\) relative to the origin. In unitvector notation, what is the resulting torque on the pebble about (a) the origin and (b) the point \((2.0 \mathrm{~m}, 0,-3.0 \mathrm{~m})\) ?

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