Gegeben sei das schwingungsfähige gedampfte Feder-Masse-System (Federpendel) mit den folgenden Kenndaten: $$ m=0,5 \mathrm{~kg}, \quad b=8 \mathrm{~kg} / \mathrm{s}, \quad c=128 \mathrm{~N} / \mathrm{m} $$ a) Wie lautet die allgemeine Lösung der Schwingungsgleichung? b) Berechnen Sie die Kreisfrequenz \(\omega_{d}\), die Frequenz \(f_{d}\) und die Schwingungsdauer \(T_{A}\) der gedämpften Schwingung. c) Wie lautet die spezielle Lösung, die den Anfangswerten \(x(0)=0,2 \mathrm{~m}\), \(v(0)=0\) genigt? Skizzieren Sie den Schwingungsverlauf.

Short Answer

Expert verified
The general solution is \( x(t) = e^{-8t} (A \cos(4t) + B \sin(4t)) \). The damped angular frequency \( \omega_d \) is 4 rad/s, the frequency \( f_d \) is 0.636 Hz, and the period \( T_A \) is 1.57 s. The specific solution is \( x(t) = e^{-8t} (0.2 \cos(4t) + 2 \sin(4t)) \).

Step by step solution

01

- Write the Differential Equation

The general differential equation for a damped mass-spring system is: \[ m \frac{d^2x}{dt^2} + b \frac{dx}{dt} + cx = 0 \] Given, \[ m = 0.5 \text{ kg}, b = 8 \text{ kg/s}, c = 128 \text { N/m} \]
02

- Solve the Characteristic Equation

Assume a solution of the form \( x(t) = e^{\beta t} \). Substituting, we get the characteristic equation: \[ 0.5\beta^2 + 8\beta + 128 = 0 \] Dividing by 0.5: \[ \beta^2 + 16\beta + 256 = 0 \] Solving this quadratic equation, we get: \[ \beta = -8 \pm 4i \] Thus, the general solution is: \[ x(t) = e^{-8t} (A \cos(4t) + B \sin(4t)) \]
03

- Calculate the Damped Angular Frequency

The damped angular frequency \( \omega_d \) is the imaginary part of the roots: \[ \omega_d = 4 \text{ rad/s} \]
04

- Calculate the Damped Frequency

The damped frequency \( f_d \) is given by: \[ f_d = \frac{\omega_d}{2\pi} = \frac{4}{2\pi} \approx 0.636 \text{ Hz} \]
05

- Calculate the Period of Damped Oscillation

The period of damped oscillation \( T_A \) is: \[ T_A = \frac{1}{f_d} \approx \frac{1}{0.636} \approx 1.57 \text{ s} \]
06

- Solve for the Specific Solution Using Initial Conditions

Given: \( x(0) = 0.2 \text{ m}, v(0) = 0 \) Substitute into the general solution: \[ x(0) = A = 0.2 \text{ m} \] Using the initial velocity condition \( v(0) = 0 \): \[ \dot{x}(0) = -8A + 4B = 0 \Rightarrow B = 2 \text{ m} \] Thus, the specific solution is: \[ x(t) = e^{-8t} (0.2 \cos(4t) + 2 \sin(4t)) \]
07

- Sketch the Solution

You can sketch the solution by plotting \( x(t) \) over time, showing the decaying oscillatory behavior due to the damping.

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Key Concepts

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

Differential Equations
Understanding differential equations is crucial for analyzing a damped harmonic oscillator. A differential equation is a type of mathematical equation that relates a function with its derivatives. In the context of a damped harmonic oscillator, the differential equation describes the motion of the mass-spring system over time.
For a damped mass-spring system, the general differential equation is: \[ m \frac{d^2x}{dt^2} + b \frac{dx}{dt} + cx = 0 \] , where: - m is the mass, - b is the damping coefficient, - c is the spring constant, - x is the displacement, - t is time.
This equation shows how the mass's motion is influenced by both spring force and damping force. Understanding how to solve this differential equation helps determine the behavior of the system.
Damped Frequency
Damped frequency, also known as the damped angular frequency, is an essential part of understanding a damped harmonic oscillator. It represents the frequency at which the system oscillates when a damping force is present.
From the characteristic equation, we find the roots which include complex numbers. These complex roots help us identify the damped frequency. In our example, the characteristic equation is: \[ 0.5\beta^2 + 8\beta + 128 = 0 \]. Solving this quadratic equation yields the roots: \[ \beta = -8 \pm 4i \] The damped angular frequency (ωd) is the imaginary part of these roots, which is 4 rad/s. Knowing the damped angular frequency allows us to calculate the damped frequency (fd) using the formula:\[ f_d = \frac{\beta_d}{2\pi} \] This calculation helps us understand the rate of oscillations in the presence of damping.
Decaying Oscillations
Decaying oscillations are a hallmark of damped harmonic oscillators. When damping is present, the amplitude of the oscillations decreases over time, eventually bringing the system to rest.
In our system, the general solution to the differential equation: \[ x(t) = e^{-8t} (A \cos(4t) + B \sin(4t)) \] demonstrates this behavior. Here, the exponential term \ e^{-8t} \ suggests that the amplitude diminishes exponentially with time. This term represents the decaying nature of the oscillations, indicating how the system loses energy due to damping.
Understanding this concept helps predict how the system’s vibrations will diminish, which is essential in various engineering and physics applications.
Mass-Spring System
A mass-spring system is a fundamental model in physics, used to illustrate simple harmonic motion and damped oscillations.
The system consists of a mass attached to a spring, where the spring provides a restoring force proportional to the displacement from the equilibrium position. The behavior of such a system is described by Hooke's law: \[ F = -kx \],where F is the restoring force, k is the spring constant, and x is the displacement. In a damped system, additional forces come into play, such as the damping force which opposes the motion and is proportional to the velocity.Analyzing a mass-spring system with damping involves solving the differential equation, \[ {{m \frac{d^2x}{dt^2} + b \frac{dx}{dt} + cx = 0}} \] , to understand how the system behaves over time. This knowledge is crucial for designing systems in engineering that need to control vibrations and ensure stability.

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Most popular questions from this chapter

Die folgenden Anfangswertprobleme beschreiben mechanische Schwingungen im aperiodischen Grenz fall. Wie lauten die L?sungen? a) \(2 \vec{x}+10 \dot{x}+12,5 x=0, \quad x(0)=5, \quad \dot{x}(0)=1\) b) \(\quad \ddot{x}+\dot{x}+0,25 x=0, \quad x(0)=1, \quad \dot{x}(0)=-1\)

Bestimmen Sie zu jeder der nachfolgenden linearen Differentialgleichungen eine partikuläre Losung: a) \(y^{\prime \prime \prime}-y^{\prime}=10 x\) b) \(y^{\prime \prime \prime}+4 y^{\prime \prime}+13 y^{\prime}=\mathrm{e}^{x}+10\) c) \(y^{\prime \prime \prime}-3 y^{\prime}+2 y=2 \cdot \cos x-3 \cdot \sin x\) d) \(x^{(4)}+2 \vec{x}+x=t \cdot \mathrm{e}^{-t}\) e) \(y^{(5)}-2 y^{(4)}+3 y^{\prime \prime \prime}-6 y^{\prime \prime}-4 y^{\prime}+8 y=\) \(=-104 \cdot e^{3 x}+24 \cdot \sin x-12 \cdot \cos x+8 x^{2}\)

Ein Pendel unterliege der periodischen Beschleunigung \(a(t)=-5 \cdot \cos t .\) Bestimmen Sie die Geschwindigkeits- Zeit-Funktion \(v=v(t)\) und die Weg-Zeit- Funktion \(s=s(t)\) fur die \(A\) nfangswerte \(s(0)=5, v(0)=0\).

Zeigen Sie, daB die Funktionen \(y_{1}=\mathrm{e}^{x}, y_{2}=\mathrm{e}^{-x}\) und \(y_{3}=\mathrm{e}^{-2 x}\) eine Fundamentalbasis der homogenen linearen Differentialgleichung 3. Ordnung $$ y^{\prime \prime \prime}+2 y^{\prime \prime}-y^{\prime}-2 y=0 $$ bilden.

In einem \(\operatorname{sog} . R L\) - Stromkreis mit einem ohmschen Widerstand \(R\) und einer Induktivität \(L\) gen?gt die Stromst?rke \(i\) der linearen Differentialgleichung \(1 .\) Ordnung $$ L \frac{d i}{d t}+R i=u $$ Dabei ist \(u=u(t)\) die von außen angelegte Spannung (Bild V-64). Bestimmen Sie den zeitlichen Verlauf der Stromstärke \(i=i(t)\) a) bei konstanter Spannung \(u(t)=\) const. \(=u_{0}\), b) bei linear mit der Zeit ansteigender Spannung \(u(t)=\) at \((a>0)\), jeweils für den Anfangswert \(i(0)=0\).

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