/*! 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 87 A uniform solid cylinder with ma... [FREE SOLUTION] | 91Ó°ÊÓ

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A uniform solid cylinder with mass \(M\) and radius 2\(R\) rests on a horizontal tabletop. A string is attached by a yoke to a frictionless axle through the center of the cylinder so that the cylinder can rotate about the axle. The string runs over a disk-shaped pulley with mass \(M\) and radius \(R\) that is mounted on a frictionless axle through its center. A block of mass \(M\) is suspended from the free end of the string (Fig. P10.87). The string doesn't slip over the pulley surface, and the cylinder rolls without slipping on the tabletop. Find the magnitude of the acceleration of the block after the system is released from rest.

Short Answer

Expert verified
The acceleration of the block is \( \frac{g}{3} \).

Step by step solution

01

Analyzing the forces and torques

Identify the forces acting on each component of the system and write the equations of motion. For the block, which is subjected to gravity, the tension in the string opposed the gravitational force. For the pulley, the net torque is due to the tension in the string, directly affecting its rotation. Finally, for the rolling cylinder, tension in the string and the frictional force influence its rotation and translational motion as it rolls without slipping.
02

Writing Equation of Motion for the Block

Apply Newton's second law to the block. Let the tension in the string be \(T\) and the gravitational force be \(Mg\). The equation becomes: \ \( Mg - T = Ma \)
03

Writing Torque Equation for the Pulley

For the pulley, use the rotational analog of Newton's second law. The tension difference on either side of the pulley, due to the block and the cylinder, creates a torque: \ \( T R = I_{pulley} \cdot \alpha \), where \( I_{pulley} = \frac{1}{2}MR^2 \) is the moment of inertia of the pulley and \( \alpha = \frac{a}{R} \) is the angular acceleration of the pulley. This simplifies to: \ \( T = \frac{1}{2}Ma \).
04

Writing Motion and Torque Equations for the Cylinder

The cylinder's translational motion can be described by: \ \( F_{friction} = Ma_{cylinder} \). The frictional force also causes rotation: \ \( F_{friction} \cdot 2R = I_{cylinder} \cdot \frac{a_{cylinder}}{2R} \), where \( I_{cylinder} = \frac{1}{2}M(2R)^2 = 2MR^2 \). Thus, the frictional force \( F_{friction} = \frac{2}{4}M a_{cylinder} = \frac{1}{2}M a_{cylinder} \).
05

Solving for the Acceleration

Set the acceleration of the block equal to the linear acceleration of the corresponding pulley string and rolling cylinder: \( a = a_{cylinder} = a_{pulley} \). Using the equations derived: \ \( T = \frac{1}{2}Ma \) from the pulley and \( Mg - T = Ma \) from the block, substitute for \(T\) to get: \ \( Mg - \frac{1}{2}Ma = Ma \). Simplifying gives \( a = \frac{g}{3} \). This is the acceleration of the block.

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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 of motion forms the backbone of classical mechanics. It states that the acceleration of an object is directly proportional to the net force acting on the object and inversely proportional to its mass. This law can be expressed by the formula: - \[ F = ma \] - where \( F \) is the net force applied, \( m \) is the mass of the object, and \( a \) is the acceleration produced.In the context of our exercise, we apply Newton's second law to the block hanging from the string. The block experiences a gravitational force downwards equal to \( Mg \), where \( g \) is the acceleration due to gravity. The tension \( T \) in the string acts upwards, creating a net force \( Mg - T \). According to Newton's second law, this net force also equals \( Ma \), where \( a \) is the acceleration of the block. This leads to the equation: - \[ Mg - T = Ma \] - Understanding this equation helps us analyze the force dynamics involved when the block begins to move.
moment of inertia
The moment of inertia is a fundamental concept in the study of rotational dynamics. It's analogous to mass in linear motion and measures how much an object resists rotational motion about a specific axis. For a rigid body, the moment of inertia \( I \) is defined as: - \[ I = rac{1}{2} MR^2 \] - for a solid disk, where \( M \) is the mass and \( R \) is the radius of the disk.In our exercise, the moment of inertia is crucial for both the pulley and the cylinder. For the pulley, which is disk-shaped, the moment of inertia is \( I_{pulley} = \frac{1}{2}MR^2 \). This value describes how the mass of the pulley is distributed relative to its axis and directly influences how torque affects its rotational acceleration.Similarly, the solid cylinder, rolling without slipping, has a moment of inertia of \( I_{cylinder} = 2MR^2 \). This indicates that the cylinder is more resistant to rotational motion compared to the pulley, as its moment of inertia includes a factor for its larger radius.
rolling without slipping
Rolling without slipping is an important concept when analyzing objects like wheels or cylinders as they move on a surface. This condition means that the point in contact with the surface is momentarily at rest as the object rolls—it does not slide across the surface.The relationship between linear and angular velocities is maintained as such:- \[ v = R\omega \] - where \( v \) is the linear velocity of the center of mass, \( R \) is the radius, and \( \omega \) is the angular velocity. This same relation exists between linear acceleration and angular acceleration:- \[ a = R\alpha \] - where \( a \) is linear acceleration and \( \alpha \) is angular acceleration.In the given task, the string does not slip over the pulley's surface, and the cylinder rolls without slipping on the tabletop. This assures us that the linear acceleration of the cylinder is linked with its angular acceleration, enabling the application of these formulas to solve for the block's acceleration.
angular acceleration
Angular acceleration describes how quickly an object's rotational speed changes with time. It is the rotational equivalent of linear acceleration. The equation for angular acceleration \( \alpha \) in terms of torque \( \tau \) and moment of inertia \( I \) is given by:- \[ \tau = I \alpha \] - In this relation, \( \alpha \) reflects the change in angular velocity.For the pulley in our exercise, as the mass is released and the system starts moving, the tension in the string exerts a torque on the pulley. The necessary equation is: - \[ T R = I_{pulley} \cdot \alpha \] - Substituting for the moment of inertia, we can find \( \alpha \) as a function of the linear acceleration \( a \) using: - \[ \alpha = \frac{a}{R} \] - This relationship helps us connect the linear movement of the block and cylinder with the rotational motion of the pulley, allowing us to calculate the overall system dynamics.

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Most popular questions from this chapter

When an object is rolling without slipping, the rolling friction force is much less the friction force when the object is sliding; a silver dollar will roll on its edge much farther than it will slide on its flat side (see Section 5.3\() .\) When an object is rolling without slipping on a horizontal surface, we can approximate the friction force to be zero, so that \(a_{x}\) and \(\alpha_{z}\) are approximately zero and \(v_{x}\) and \(\omega_{z}\) are approximately constant. Rolling without slipping means \(v_{x}=r \omega_{z}\) and \(a_{x}=r \alpha_{z}\) . If an object is set in motion on a surface without these equalities, sliding (kinetic) friction will act on the object as it slips until rolling without slipping is established. A solid cylinder with mass \(M\) and radius \(R\) , rotating with angular speed \(\omega_{0}\) about an axis through its center, is set on a horizontal speed \(\omega_{0}\) about the kinetic friction coefficient is \(\mu_{\mathrm{k}}\) (a) Draw a free-body diagram for the cylinder on the surface. Think carefully about the direction of the kinetic friction force. on the cylinder. Calculate the accelerations \(a_{x}\) of the center of mass and \(\alpha_{z}\) of rotation about the center of mass. (b) The cylinder is initially slipping completely, so initially \(\omega_{z}=\omega_{0}\) but \(v_{x}=0 .\) Rolling without slipping sets in when \(v_{x}=R \omega_{z} .\) Calculate the distance the cylinder rolls before slipping stops. (c) Calculate the work done by the friction force on the cylinder as it moves from where it was set down to where it begins to roll without slipping.

An engine delivers 175 hp to an aircraft propeller at 2400 rev/min. (a) How much torque does the aircraft engine provide? (b) How much work does the engine do in one revolution of the propeller?

A uniform rod of length \(L\) rests on a frictionless horizontal surface. The rod pivots about a fixed frictionless axis at one end. The rod is initially at rest. A bullet traveling parallel to the horizontal surface and perpendicular to the rod with speed \(v\) strikes the rod at its center and becomes embedded in it. The mass of the bullet is one-fourth the mass of the rod. (a) What is the final angeed of the rod? (b) What is the ratio of the kinetic energy of the system after the collision to the kinetic energy of the bullet before the collision?

A \(500.0-\mathrm{g}\) bird is flying horizontally at 2.25 \(\mathrm{m} / \mathrm{s}\) not paying much attention, when it suddenly flies into a stationary vertical bar, hitting it 25.0 \(\mathrm{cm}\) below the top (Fig. P10.95). The bar is uniform, 0.750 \(\mathrm{m}\) long, has a mass of \(1.50 \mathrm{kg},\) and is hinged at its base. The collision stuns the bird so that it just drops to the ground afterward (but soon recovers to fly happily away). What is the angular velocity of the bar (a) just after it is hit by the bird and (b) just as it reaches the ground?

A cord is wrapped around the rim of a solid uniform wheel 0.250 \(\mathrm{m}\) in radius and of mass 9.20 \(\mathrm{kg} .\) A steady horizontal pull of 40.0 \(\mathrm{N}\) to the right is exerted on the cord, pulling it off tangentially from the wheel. The wheel is mounted on frictionless bearings on a horizontal axle through its center. (a) Compute the angular acceleration of the wheel and the acceleration of the part of the cord that has already been pulled off the wheel. (b) Find the magnitude and direction of the force that the axle exerts on the wheel. (c) Which of the answers in parts (a) and (b) would change if the pull were upward instead of horizontal?

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