Find the inverse Laplace transform of: $$\frac{1}{\left(p^{2}+a^{2}\right)^{3}}$$

Short Answer

Expert verified
\( \mathcal{L}^{-1} \left\{ \frac{1}{\left(p^{2}+a^{2}\right)^{3}} \right\} = \frac{t^{2}\sin(at)}{2a^{3}} \)

Step by step solution

01

Identify the standard form

The given function is \(\frac{1}{\big(p^{2}+a^{2}\big)^{3}}\). This resembles a standard Laplace transform form related to \(\frac{t^{n}}{n!} \text{ with inverse } \frac{1}{p^{n+1}}\).
02

Recognize the relevant inverse Laplace form

From the Laplace transform tables, it's known that \(\frac{t^{2}}{2!}\frac{\text{sin}(at)}{a^{3}} \text{ has the inverse transform} \frac{1}{(p^2 + a^2)^3}\).
03

Apply the inverse transform

Given \(\frac{1}{\big(p^{2}+a^{2}\big)^{3}}\), we can identify the inverse by using the standard form \(\frac{t^{2} \text{ sin}(at)}{2! \times a^{3}}\). Thus, the inverse Laplace transform is \(\frac{t^2 \text{sin}(at)}{2a^3} \text{ for the } p \text{-domain function } \frac{1}{(p^2 + a^2)^3}\).

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Key Concepts

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

Laplace transform
The Laplace transform is a powerful mathematical tool used to transform functions from the time domain to the frequency domain. This technique is especially useful in solving differential equations and analyzing linear systems. In essence, if you have a function of time, say \(f(t)\), the Laplace transform of this function, denoted as \(F(p)\), is obtained through the integral: \[ F(p) = \int_{0}^{\infty} e^{-pt} f(t) dt \] Here, \(p\) is a complex number. The main advantage of using the Laplace transform is that it converts differential equations into algebraic equations, which are usually easier to solve. Once you solve for \(F(p)\), you can then use the inverse Laplace transform to convert back to the time domain.
Inverse transform
Inverse Laplace transform allows us to convert back from the frequency domain to the time domain. It is denoted by \(L^{-1}\) and retrieves the original function \(f(t)\) given its Laplace transform \(F(p)\). For example, if you have \[ F(p) = \frac{1}{(p^2 + a^2)^3} \], using the inverse Laplace transform table, we can identify the corresponding time function. In this instance, the solution is: \[ L^{-1} \left\{ F(p) \right\} = \frac{t^2 \text{sin}(at)}{2a^3} \] Recognizing the standard forms and using the tables is key to simplifying this process. It essentially involves matching the given function with known forms and then applying the inverse forms directly.
Standard forms
Standard forms play a significant role in simplifying the computation of Laplace and inverse Laplace transforms. These forms create a rulebook, making it easier to match given functions to their time or frequency domain counterparts. Some common standard forms include:
  • \(L \left \{1\right \} = \frac{1}{p} \)
  • \(L \left \{t\right \} = \frac{1}{p^2} \)
  • \(L \left \{e^{at}\right \} = \frac{1}{p-a} \)
For example, in the given problem, \[ L^{-1} \left \{ \frac{1}{(p^2 + a^2)^3} \} = \frac{t^2 \text{sin}(at)}{2a^3} \] Recognizing these forms streamlines the solving process, allowing you to focus on the algebraic manipulation. Always keep standard forms handy while working with Laplace transforms.

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Most popular questions from this chapter

By using Laplace transforms, solve the following differential equations subject to the given initial conditions. $$y^{\prime \prime}+y^{\prime}-5 y=e^{2 t}, \quad y_{0}=1, y_{0}^{\prime}=2$$

Show that the thickness of the ice on a lake increases with the square root of the time in cold weather, making the following simplifying assumptions. Let the water temperature be a constant \(10^{\circ} \mathrm{C},\) the air temperature a constant \(-10^{\circ},\) and assume that at any given time the ice forms a slab of uniform thickness \(x\). The rate of formation of ice is proportional to the rate at which heat is transferred from the water to the air. Let \(t=0\) when \(x=0.\)

(a) A rocket of (variable) mass \(m\) is propelled by steadily ejecting part of its mass at velocity \(u\) (constant with respect to the rocket). Neglecting gravity, the differential equation of the rocket is \(m(d v / d m)=-u\) as long as \(v \ll c, c=\) speed of light. Find \(v\) as a function of \(m\) if \(m=m_{0}\) when \(v=0\). (b) In the relativistic region ( \(v / c\) not negligible), the rocket equation is \(m \frac{d v}{d m}=-u\left(1-\frac{v^{2}}{c^{2}}\right)\). Solve this differential equation to find \(v\) as a function of \(m .\) Show that \(v / c=\) \((1-x) /(1+x),\) where \(x=\left(m / m_{0}\right)^{2 u / c}\).

Solve the algebraic equation $$D^{2}+(1+2 i) D+i-1=0$$ (note the complex coefficients) and observe that the roots are complex but not complex conjugates. Show that the method of solution of (5.6) (case of unequal roots) is correct here, and so find the general solution of $$y^{\prime \prime}+(1+2 i) y^{\prime}+(i-1) y=0$$

Heat is escaping at a constant rate \([d Q / d t \text { in }(1.1) \text { is constant }]\) through the walls of a long cylindrical pipe. Find the temperature \(T\) at a distance \(r\) from the axis of the cylinder if the inside wall has radius \(r=1\) and temperature \(T=100\) and the outside wall has \(r=2\) and \(T=0.\)

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