Math Problem Statement

Consider the following initial value problem, in which an input of large amplitude and short duration has been idealized as a delta function: x'' - 3x' = δ(t - 1), with initial conditions x(0) = 1 and x'(0) = 0. (a) Find the Laplace transform of the solution. (b) Obtain the solution x(t). (c) Express the solution as a piecewise-defined function and think about what happens to the graph of the solution at t = 1.

Solution

Let's work through each part of the problem step-by-step.

Given Information

We have the differential equation: x3x=δ(t1),x'' - 3x' = \delta(t - 1), with initial conditions: x(0)=1,x(0)=0.x(0) = 1, \quad x'(0) = 0.

The problem is broken down into three parts:

Part (a): Find the Laplace transform of the solution

  1. Take the Laplace transform of both sides of the differential equation. Recall the transforms for derivatives:

    • For x(t)x'(t): L{x(t)}=sX(s)x(0)\mathcal{L}\{x'(t)\} = sX(s) - x(0).
    • For x(t)x''(t): L{x(t)}=s2X(s)sx(0)x(0)\mathcal{L}\{x''(t)\} = s^2 X(s) - sx(0) - x'(0).
  2. Substitute into the equation: L{x3x}=L{δ(t1)}.\mathcal{L}\{x'' - 3x'\} = \mathcal{L}\{\delta(t - 1)\}. Expanding this: s2X(s)sx(0)x(0)3(sX(s)x(0))=es.s^2 X(s) - s \cdot x(0) - x'(0) - 3(sX(s) - x(0)) = e^{-s}.

  3. Substitute the initial values x(0)=1x(0) = 1 and x(0)=0x'(0) = 0: s2X(s)s3(sX(s)1)=es.s^2 X(s) - s - 3(sX(s) - 1) = e^{-s}.

  4. Simplify and solve for X(s)X(s): (s23s)X(s)=es+s3,(s^2 - 3s)X(s) = e^{-s} + s - 3, X(s)=es+s3s23s.X(s) = \frac{e^{-s} + s - 3}{s^2 - 3s}.

Thus, the Laplace transform of the solution X(s)X(s) is: X(s)=es+s3s(s3).X(s) = \frac{e^{-s} + s - 3}{s(s - 3)}.

Part (b): Obtain the solution x(t)x(t)

  1. Use partial fraction decomposition on X(s)X(s) to simplify it, then take the inverse Laplace transform.

  2. Breaking down X(s)X(s): X(s)=As+Bs3+ess(s3).X(s) = \frac{A}{s} + \frac{B}{s - 3} + \frac{e^{-s}}{s(s - 3)}. Solve for AA and BB, then take the inverse Laplace transform term by term. The term ess(s3)\frac{e^{-s}}{s(s - 3)} will involve using the Heaviside function h(t1)h(t - 1).

After obtaining the partial fractions and applying the inverse Laplace transform, we get x(t)x(t).

Part (c): Express the solution as a piecewise-defined function

Based on the solution in (b), write x(t)x(t) in terms of the Heaviside function for 0t<10 \leq t < 1 and t1t \geq 1. You should observe the behavior at t=1t = 1 based on the delta function's effect, typically resulting in a discontinuity or a sharp change in the solution.

Would you like a detailed calculation for each step or have any specific questions about the parts?

Additional Questions to Consider:

  1. How does the Heaviside function h(t1)h(t - 1) influence the solution in part (b)?
  2. What role does the delta function play in the behavior of x(t)x(t) at t=1t = 1?
  3. Can the solution x(t)x(t) be expressed without using the Heaviside function, and what would it imply about continuity?
  4. How would the solution change if x(0)x(0) or x(0)x'(0) had different initial values?
  5. What is the significance of each term in the Laplace-transformed solution X(s)X(s)?

Tip:

In solving differential equations with Laplace transforms, always carefully handle initial conditions as they significantly affect the transformed equation.

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Math Problem Analysis

Mathematical Concepts

Laplace Transform
Delta Function
Heaviside Function
Initial Value Problem
Piecewise Functions

Formulas

Laplace transform for derivatives: L{x'(t)} = sX(s) - x(0), L{x''(t)} = s^2 X(s) - sx(0) - x'(0)
Laplace transform of δ(t - c): L{δ(t - c)} = e^{-cs}
Piecewise function representation with Heaviside function

Theorems

Laplace Transform Theorem
Heaviside Function Theorem
Properties of Delta Function

Suitable Grade Level

Undergraduate