/*! 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 42 A block which has a mass \(m\) i... [FREE SOLUTION] | 91Ó°ÊÓ

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A block which has a mass \(m\) is suspended from a spring having a stiffness \(k .\) If an impressed downward vertical force \(F=F_{O}\) acts on the weight, determine the equation which describes the position of the block as a function of time.

Short Answer

Expert verified
The equation that describes the position of the block as a function of time is \( x(t) = A\cdot\cos(\sqrt{\frac{k}{m}}\cdot t + B) + \frac{F_0}{k} \), with A and B being constants determined by the initial conditions.

Step by step solution

01

Apply Newton's Second Law

Newton's second law says that the force on an object is equal to its mass times its acceleration. We can express this in the following differential equation for the position of the block x(t) with respect to time t: \( m\cdot \frac{d^2x}{dt^2} = -k\cdot x + F_0 \). This equation states that the product of the mass m and the second derivative of x with respect to time equals the sum of the product of the stiffness k and the position x (pointing downwards, representing the spring force), and the external force \(F_0\).
02

Simplify the Equation

Rearranging the differential equation we get: \( \frac{d^2x}{dt^2} = -\frac{k}{m} \cdot x + \frac{F_0}{m} \). This equation is a second order homogeneous differential equation with constant coefficients.
03

Identify the Form of the Solution

The general form of the solution for such a differential equation is: \( x(t) = A\cdot\cos(\sqrt{\frac{k}{m}}\cdot t + B) + \frac{F_0}{k} \), where A and B are constants to be determined by the initial conditions.

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Key Concepts

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

Differential Equation
In physics, differential equations are used to describe the relationship between a function and its derivatives. They are incredibly useful for modeling situations where change occurs over time, such as velocity or position. In the given problem, we derive a differential equation from Newton's Second Law to find the position of a block attached to a spring. This second-order differential equation is given by:
  • \( m\cdot \frac{d^2x}{dt^2} = -k\cdot x + F_0 \)
This equation tells us that the force acting on our block is balanced by a combination of the spring's force and an external force. To solve this, you must understand how to integrate these equations, which involves finding a function that can model how the block's position changes over time. The solution is vital for predicting the dynamical behavior of systems in mechanics, effortlessly marrying mathematics with real-world physical systems.
Solving such a differential equation allows us to unlock the description of motion for the system, creating a model to predict future behavior based on initial conditions.
Mass-Spring System
A mass-spring system is a classic physics model used to represent a mass attached to a spring that can oscillate vertically or horizontally. This type of system can demonstrate simple harmonic motion when displaced from its equilibrium position.The equation:
  • \( \frac{d^2x}{dt^2} = -\frac{k}{m} \cdot x + \frac{F_0}{m} \)
helps to describe how the spring force attempts to return the mass to equilibrium, while the additional force affects its motion. The constant \(k\), known as the stiffness or spring constant, quantifies how easily the spring deforms. A larger spring constant means the spring is stiffer, storing more energy for the same displacement, thus generating a stronger force. Mass \(m\) represents the inertia of the block. Other variables like initial displacement and velocity also influence the system's motion. Understanding such a system is fundamental in engineering and physics, revealing how outside forces can affect equilibrium.
Harmonic Motion
Harmonic motion, especially when focusing on simple harmonic motion (SHM), refers to a type of periodic motion where the restoring force is directly proportional to the displacement. This model applies precisely to our mass-spring system when the external force is absent. But when an external force is present, it slightly modifies the pure SHM model, resulting in forced vibration.The solution:
  • \( x(t) = A\cdot\cos(\sqrt{\frac{k}{m}}\cdot t + B) + \frac{F_0}{k} \)
illustrates both the natural oscillation term and the steady state induced by the force. Here, \(A\) and \(B\) are constants that depend on the system's initial conditions. These initial conditions will define the initial displacement and velocity, significantly impacting the oscillation characteristics. Such insights impart a deeper understanding of vibrant systems in nature, engineering, and technology that oscillate, such as bridges, vehicle suspensions, and electronic signals.

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Most popular questions from this chapter

If the lower end of the 6 -kg slender rod is displaced a small amount and released from rest, determine the natural frequency of vibration. Each spring has a stiffness of \(k=200 \mathrm{N} / \mathrm{m}\) and is unstretched when the rod is hanging vertically.

A spring has a stiffness of \(800 \mathrm{N} / \mathrm{m}\). If a 2 -kg block is attached to the spring, pushed \(50 \mathrm{mm}\) above its equilibrium position, and released from rest, determine the equation that describes the block's motion. Assume that positive displacement is downward.

An 8 -kg block is suspended from a spring having a stiffness \(k=80 \mathrm{N} / \mathrm{m} .\) If the block is given an upward velocity of \(0.4 \mathrm{m} / \mathrm{s}\) when it is \(90 \mathrm{mm}\) above its equilibrium position, determine the equation which describes the motion and the maximum upward displacement of the block measured from the equilibrium position. Assume that positive displacement is measured downward.

A block of mass \(m\) is suspended from two springs having a stiffness of \(k_{1}\) and \(k_{2},\) arranged a ) parallel to each other, and b) as a series. Determine the equivalent stiffness of a single spring with the same oscillation characteristics and the period of oscillation for each case.

The 200 -lb electric motor is fastened to the midpoint of the simply supported beam. It is found that the beam deflects 2 in. when the motor is not running. The motor turns an eccentric flywheel which is equivalent to an unbalanced weight of 1 lb located 5 in. from the axis of rotation. If the motor is turning at 100 rpm, determine the amplitude of steady-state vibration. The damping factor is \(c / c_{c}=0.20 .\) Neglect the mass of the beam.

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