Question

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

Short answer

The inverse Laplace transform of \(\frac{p^{2}}{(p^{2}+a^{2}\right)^{2}}\) is \(\frac{t \sin(at)}{2a}\frac{t \sin(at)}{2a}\right\).

Step-by-step solution

Identify the Form

Recognize that \(\frac{p^{2}}{\left(p^{2}+a^{2}\right)^{2}}\) resembles a standard form involving inverse Laplace transforms of rational functions.

Use a Known Inverse Laplace Transform

Recall the known Laplace transform \(\frac{t \sin(at)}{2a}\) which corresponds to \(\frac{p^{2}}{(p^2 + a^2)^2}\) from Laplace transform tables. It helps to know that the inverse Laplace transform of \(\frac{p^{2}}{(p^2 + a^2)^2}\) is \(\frac{t \sin(at)}{2a}\).

Write the Inverse Laplace Transform

Using the identified formula, the inverse Laplace transform of \(\frac{p^{2}}{(p^2 + a^2)^2}\) is: \[\frac{t \sin(at)}{2a}\frac{t \sin(at)}{2a}\].

Key concepts

Laplace transform

The Laplace transform is a powerful mathematical tool used to convert complex functions from the time domain to the s-domain, making them easier to analyze and manipulate. This transformation is particularly handy for solving differential equations and control system problems.
The Laplace transform of a function \(f(t)\) is represented as \(F(p)\), and is defined by the integral:
\[ F(p) = \int_{0}^{\infty} e^{-pt} f(t) dt \]
Here's why the Laplace transform is essential:

• It simplifies differential equations to algebraic equations.
• It handles initial and boundary conditions elegantly.
• It unifies the study of continuous and discrete-time signals.

In this exercise, we work with the Laplace transform to find its inverse, converting it back from the s-domain to the time domain.

Rational functions

Rational functions are expressions that represent the ratio of two polynomials. They are essential in Laplace transforms because most functions we deal with can be expressed this way.
Consider a rational function:
\[ R(p) = \frac{P(p)}{Q(p)} \]
where \(P(p)\) and \(Q(p)\) are polynomials. In the given problem,\[ \frac{p^{2}}{(p^2 + a^2)^2} \]
is a rational function. These forms simplify the process of finding inverse Laplace transforms because they often correspond to well-known functions in the time domain.
The proper selection and manipulation of rational functions allow us to use pre-existing tables and formulas to find inverse transforms efficiently.

Sinusoidal functions

Sinusoidal functions, including sine and cosine waves, are fundamental in the study of oscillatory systems. These functions form the backbone of many physical phenomena like electrical circuits and mechanical vibrations.
In the given exercise, we use the sinusoidal function \(\sin(at)\) in the inverse Laplace transform:
\[ \frac{t \sin(at)}{2a} \]
Here's a quick refresher:

• Sine function gives the vertical position of a point on a unit circle.
• Its Laplace transform is useful in solving systems involving periodic or oscillatory inputs.

In the exercise, recognizing the standard inverse Laplace form associated with sinusoidal functions is crucial. It's \frac{t \sin(at)}{2a}\. Knowing this helps reduce complex rational functions into more usable forms in the time domain.

Transform tables

Transform tables are invaluable resources that list common Laplace transforms and their inverses. They allow us to quickly identify the time domain function corresponding to a given s-domain function.
The table helps identify the inverse of:
\[ \frac{p^2}{(p^2 + a^2)^2} \]
as \( \frac{t \sin(at)}{2a} \). This identification streamlines the process of finding inverse Laplace transforms, making it much simpler to tackle complex problems.
Transform tables act as a reference guide, saving time and reducing errors by presenting standardized pairs of functions. They cover a broad range of functions including exponential, sinusoidal, and polynomial forms, each of which is common in practical applications and theoretical problems alike.