Laplace transform Definition and 779 Threads

In mathematics, the Laplace transform, named after its inventor Pierre-Simon Laplace (), is an integral transform that converts a function of a real variable



t


{\displaystyle t}
(often time) to a function of a complex variable



s


{\displaystyle s}
(complex frequency). The transform has many applications in science and engineering because it is a tool for solving differential equations. In particular, it transforms linear differential equations into algebraic equations and convolution into multiplication.For suitable functions f, the Laplace transform is the integral






L


{
f
}
(
s
)
=



0





f
(
t
)

e


s
t



d
t
.


{\displaystyle {\mathcal {L}}\{f\}(s)=\int _{0}^{\infty }f(t)e^{-st}\,dt.}

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  1. X

    Laplace Transform of t*u(t-1): Get Help Now!

    Homework Statement Find the laplace transform of; t*u(t-1) I always thought that the laplace transform of the function was; (1/s^2) * (e^-s) However, recently I was told that I was wrong! I was told that I was wrong, because t*u(t-1) is not a function of (t-1). That in order...
  2. J

    Transforming a Second Order Differential Equation Using Laplace Transforms

    Homework Statement Solve by Laplace transforms the following y'' + y = t when 0</=t<1, and = 1 if t>/=1 Homework Equations L{y''} + L{y} = L{f(t)} The Attempt at a Solution By Laplace transforms I get L{f(t)} = (1 - e^-s) / s^2 and Y(s) = (1-e^-2 + s^2) / s^2 (s^2 +1) But I cannot...
  3. J

    Understanding the Laplace Transform of a Complex Function

    What is y = L{Y(s)} for Y(s) = (1 - e^-s + s^2) / (s^4 + s^2)? Note: F(s) = L{f(t)} = (1 - e^-s) / s^2 I've just been going in circles trying to figure this one out. I tried simplifying it by partial fractions, but I still couldn't figure it out, and I'd appreciate some help.
  4. T

    Solving PDE with Laplace Transform

    Homework Statement \frac{\partial^{2}u}{\partial t^{2}} = a^{2} \frac{\partial^{2}u}{\partial x^{2}} (x>0, t>0) with u(0,t) = t, u(x,0) = 0, ut(x,0) = A. Solve the PDE using laplace transform. The Attempt at a Solution I have managed to get the transform: \frac{\partial^{2}U(x,s)}{\partial...
  5. S

    Bessel's equation and laplace transform

    Homework Statement Bessel's equation of order zero can be written xy''+y'+xy=0 Homework Equations Denote the solution which is finite a the origin by J0 Show that the Laplace transform of J0 is proportional to (s^2+1)^-1/2 The Attempt at a Solution
  6. J

    Laplace Transform Solution for x"+2x'+x=sin(t) x=x'=0

    Homework Statement Problem: laplace transform of x"+2x'+x=sin(t) x=x'=0 Homework Equations The Attempt at a Solution Attempt at problem: I was able to get Y(s)=1/(s^2+1)(s^2+2s+5) and then i expanded it to get [s/10(s^2+2s+5)]-[s/10(s^2+1)]+[1/5(s^2+1)]. The last two terms are...
  7. F

    How to inverse the Laplace Transform?

    Hi, I know that in order to inverse a function f(s) back to its time domain counterpart, f(t), one must use the line integral, the Bromwich Integral, but I do not know how to evaluate a line integral. Does anyone know of any practical methods of evaluating the inverse Laplace transform, could...
  8. T

    Laplace Transform of t u(t-2) using Basic Definition

    Homework Statement find the laplace transform of g(t) = t u(t-2) using the basic definition. Homework Equations L{f(t)} = ∫f(t)e-stdt from 0 to infinity The Attempt at a Solution I am able to get the transform by applying the t-shifting property. However, how do I do it by using...
  9. 2

    Converting et*u1(t) to F(s) using Laplace Transform

    Homework Statement If I had something like, et*u1(t), how would I convert it to F(s) Homework Equations ua(t)*f(t-a) = e-asF(s) The Attempt at a Solution From the general equation of transformation, I don't have f(t-a) and I don't think I can make one out of the exponential...
  10. G

    Finding g(t) with Laplace Transform of G(S)

    G(S)=2/s(e^-3s_e^-4s) G(S)=(2S+1/S^2)*e^-2s_(3s+1/s^2)*e-3s find g(t)?
  11. K

    The proof of Time Scaling, Laplace transform

    Hi I understand most of the steps in the determination of the time scale. But i don't really understand the step in equation 6.96. The first attachment is the full details of the time scale, and the second attachment is the part which I am stuck on. I just want to know, how they get...
  12. 2

    Inverse Laplace Transform for F(s): Is it Possible?

    Homework Statement Is it possible to do the inverse laplace transform for this? F(s) = \Sigma[e^(ns)]/s where n=0 and goes to infinity Homework Equations u_c(t) = [e^-(cs)]/s The Attempt at a Solution I don't think I can use this conversion because c or s is never less than...
  13. H

    Damped HO and Laplace transform method

    Hi, I am trying to solve the damped harmonic oscillator: \frac{d^2y}{dt^2}+\frac{b}{m} \frac{dy}{dt}+\frac{k}{m}y=0 and I thought using the Laplace transform might do the trick. Anyway so I did the LT (and inserted the initial conditions that at t=0 y=A, and dy/dt=0) and obtained...
  14. T

    What is the Laplace Transform of a Derivative Function?

    (d^n/dt^n)f(t)= ?? im not entirely sure how to solve this problem...
  15. Q

    Inverse Laplace Transform: Solving for Coefficients and Completing the Square

    Homework Statement Determine the inverse Laplace transform of 1/((s^2 +1)*(s-1)). The answer is 1/2*(e^x - cos(x) - sin(x)). Homework Equations We get a table of known inverse Laplace transforms. The Attempt at a Solution I tried to break this up using partial fractions...
  16. W

    Help with an easy Laplace Transform problem.

    Problem; If, f(t) = d/dt [(e^-5t) (cos2t)] Find F(s). Eh, well, I don't really know what to do, can I get some pointers? Am I supposed to integrate both sides, so I can get rid of d/dt, and then apply the integration property to find the answer?
  17. W

    Laplace transform (solve an IVP)

    Homework Statement Solve the IVP for t>0 y'(t)+\int^{t}_{0}y(\tau)d\tau = =sin(t) for 0<t<=pi =0 for t>pi y(0)=-1 The Attempt at a Solution The solution depends on how large t is and therefore the solution consist of two parts depending on the size of t.. Let's call them y1(t)...
  18. C

    Laplace transform of sin(ωt – Φ)

    Hi, I'm doing some preparation work for an upcoming mathematics module at University and I'm going over some Laplace transform questions. Part of one question asks for the Laplace transform of sin(ωt – Φ) and after looking the transform up I've found the answer to be (ω)cos(Φ) + (s)sin(Φ)...
  19. C

    How can I prove the Laplace transform of t^n step by step?

    I know the final result, its on all the charts. But I need to show step by step how to get the solution. If someone could help out by getting me in the right direction or just plain giving me the answer, that would be much appreciated:smile:.
  20. S

    An infinite series transformed from Laplace transform

    hello. I have transformed the Laplace transform into the infinite series by repeatedly using integration by parts. What is this infinite series? may be Laplace transform series, or only an infinite series without name? L(t)= \int_{t}^{\infty}\frac{f(t)}{e^{st}} dt =-0 +...
  21. A

    Finding Inverse Functions Using Laplace Transform

    Ok i have two questions, one i am unsure of and one i don't have a clue how to correctly find it. Homework Statement You have to work out the inverse function of: 4s/ s^2+4s+8 The Attempt at a Solution I think the answer is: 4e^(-2t)*(cos2t+sin2t) Is this correct? Homework...
  22. M

    What is the Inverse Laplace Transform of (s+1)/ (s^2 + 4s + 5) + e^-2s / 3s^4?

    Homework Statement Find the inverse laplace transform of (s+1)/ (s^2 + 4s + 5) + e^-2s / 3s^4 Homework Equations The Attempt at a Solution For the first one (s+1) / (s^2 + 4s + 5), I completed the square for the denominator so (s+1) / [(s+1)^2 + 1] Now it gets...
  23. L

    Laplace Transform - Step Functions

    Homework Statement Please help by explaining in detail how to find the Laplace transform of the function f(t) = { 2 0 <= t < 3 { -2 t >= 3. Homework Equations The Attempt at a Solution For the most part I know that U(t-3)(t-3). I want to account for the amplitude...
  24. E

    Solving Laplace Transforms: x'' + 2x' + 5x = 3e^{-t}cos(2t)

    I hope somebody's up tonight, this is due in the morning and I'm so close. So I was assigned to solve this differential equation using laplace transforms and although I (think I) can solve it, I'm not getting the same answer that Maple spits out. The DE is: x'' + 2x' + 5x =...
  25. M

    How Do You Use the Unit Step Function to Find the Laplace Transform of g(t)?

    Homework Statement This has to do with the unit step function. The question is; Sketch the function g(t) = 1 for 0<t<1 and is 0 for t>1. Express g(t) in terms of the unit step function and hence or otherwise show that L(g(t)) = 1/s^2 - e^-s (1/s^2 + 1/2) Homework Equations...
  26. J

    Laplace Transform equation help

    [SOLVED] Laplace Transform Homework Statement Suppose F(s) = \displaystyle\mathcal{L}(f(t)) Show that \displaystyle\mathcal{L}(f(ct)) = 1/c F(s/c) Homework Equations The Attempt at a Solution \displaystyle\mathcal{L}(f(t)) = \int_0^{inf} e^{-st} f(t) dt \displaystyle\mathcal{L}(f(ct)) =...
  27. J

    Solved: Inverse Laplace Transform of $\frac{e^{-2s}}{s^2+s-2}$

    [SOLVED] Laplace transform Homework Statement Find the inverse laplace transform of \frac{e^{-2s} }{s^2 + s - 2} Homework Equations The Attempt at a Solution I'm able to do about half of the problem using partial fractions, I've found...
  28. M

    Can Laplace Transform Prove f(t) = O(t) for a Given Integral Equation?

    let be a function f(t) , and i want to prove that f(t)=O(t) in big-O notation. i know that Laplace transform of f(t) is F(s) then i perform the integral F(s)= \int_{0}^{\infty} dt f(t) e^{-st} if we assume f(t)=O(t) then F(s)= \int_{0}^{\infty} dt f(t) e^{-st} \le \int_{0}^{\infty}...
  29. G

    How Do You Graph the Inverse Laplace Transform of a Piecewise Function?

    Homework Statement determine the inverse laplace transform f(t) of the function Homework Equations F(s) = 3/s - (4e^-s)/s^2 + (5e^-2s)/s^2 The Attempt at a Solution i broke it up into the 3 part and got them seperatly which gave me f(t) = 3 - 4u(t-1)(t-1) + 5u(t-2)(t-2)...
  30. N

    How do I find the inverse Laplace Transform of a complex function?

    My goodness.. I have not come across an inverse Laplace transform like this. My teacher let's us just use a chart to figure them out, but this is definitely not on there. How do I find the inverse Laplace transform of: { (1/2)+[(5e^-6s)/(4s^2)] } / (s+5) I already used partial fractions to...
  31. T

    Need help with an integral: Laplace Transform of a chirp

    I am trying to find the Laplace Transform of a chirp: Essentially this requires evaluating an integral between zero and infinity of: (exp(s*t))*sin(t^2) with respect to t where s is the parameter (Laplace space frequency). Any help or advice or a redirect to some useful link would be much...
  32. H

    Laplace transform, book example

    [SOLVED] Laplace transform, book example I'm having trouble following one of the steps in my textbook. They give a function: y(t) = e^{2t} and plug it into Y(s) = \int_{0}^{\infty} y(t) e^{-st} dt and compute. They end up with: \frac{1}{2-s} \underbrace{lim}_{b -> \infty} e^{(2-s)b}...
  33. R

    What is the Laplace transform of sin2tcos2t?

    iv got a problem i can't seem to understand. if anyone could help me out it would be great f(t)= sin2tcos2t im just not sure what to do when i have the product of 2 trig functions. the correct answer is (2/(s^2 + 16)) thanks for any help
  34. E

    How Do You Solve This Laplace Transform Problem?

    [SOLVED] Laplace Transform question Homework Statement Use the Laplace transform to solve the given IVp {\frac {d^{2}}{d{t}^{2}}}y \left( t \right) +2\,{\frac {d}{dt}}y \left( t \right) +5\,y \left( t \right) ={e^{-t}}\sin \left( 2\,t \right) y(0)=1, y'(0)=-1Homework Equations L(f) =...
  35. E

    How Do You Solve an Inverse Laplace Transform Problem?

    Hello Guys, I have three Inverse Laplace problem that is troubling me literary.. I'm trying to solve it but i just can't figured it out.. Can you please provide a detailed solution on how you arrived on the answer that you going to give, so i can study it and how to do it.. Attached...
  36. Saladsamurai

    Laplace Transform (Should be easy)

    [SOLVED] Laplace Transform (Should be easy) Homework Statement I know there are other ways to solve this, but I HAVE to use Laplace Transformy''-y'-6y=0 where y(0)=2 and y'(0)=-1The Attempt at a Solution Written as Laplace: y''-y'-6y=0 \Rightarrow...
  37. T

    Laplace Transform f(t) = e^t *sin(t)sin(5t)

    Hey everyone Does anyone know how to do the following Laplace Transformation f(t) = e^t *sin(t)sin(5t) i can do it with one sin function but don't know how to do it with 2. any help would be appreciated.
  38. K

    Laplace Transform F(s) = s/((s^2)+2s+10)

    Homework Statement Inverse Laplace Transform of given, F(s) = s/((s^2)+2s+10) Homework Equations n/a The Attempt at a Solution I reduced it down to s/(((s+1)^2)+9) but I can't find the proper form of it, meaning I have to reduce is a little bit more but I can't think of a way to...
  39. J

    Solve Laplace Transform of t sinwt w/ Theorem 1.31

    Homework Statement Determine L{t sinwt} with the aid of therom 1.31 (its the General Differentiation method on this page: [PLAIN]"link"[/URL] Homework Equations Shown on linked page The Attempt at a Solution I do not understand how to start this becasue I do not have a...
  40. J

    Laplace transform of f(x)= xcos(ax)

    Homework Statement Laplace transform from f(x) = x cos(ax) to ^f(s) = (s^2 - a^2) / (s^2 + a^2)^2 how do you get the -a^2 term in the numerator, all i come up with is s^2? Homework Equations f(x) = x e^(ax) ----> ^f(s) = 1/(s-a)^2 2 cos(ax) = e^(aix) + e^(-aix) The Attempt...
  41. T

    Applied example of Laplace Transform?

    I'm looking some applied example of Laplace transform. For instance: If I have function f(t) = Asin(ωt + φ), where; A is peak deviation from center ω is Angular velocity t is time φ is phase and now I want to laplace transform it and get some function like...
  42. P

    What is the Inverse Laplace Transform for V(s)=\frac{2s}{(s^{2}+4)^{2}}?

    1. Find v(t) if V(s)=\frac{2s}{(s^{2}+4)^{2}} Ans: v(t)=\frac{1}{2}tsin2tu(t) 2. Homework Equations : V(s)=\frac{a_{n}}{(s-p)^{n}}+\frac{a_{n-1}}{(s-p)^{n-1}}+\cdots+\frac{a_{1}}{(s-p)} a_{n-k}=\frac{1}{k!}\frac{d^{k}}{ds^{k}}[(s-p)^{n}V(s)]_{s=p} 3. Attempt at a solution...
  43. O

    Proof of the convolution theorem for laplace transform

    My textbook provides a proof but there's one thing about the proof i do not understand it starts assuming L{f(t)} = the laplace integral with the f(t) changed to f(a) same goes with L{g(t)} as it changes it to g(b) i understand the big picture>>starting from a product of 2 L transforms...
  44. J

    Inverse Laplace Transform - Step Function?

    Given... (2s^{2}+1)e^{-s} ------------------ (s - 1)(s^{2} + 4s + 5) Find the inverse Laplace Transform. I am unsure where to start and am just looking for a little direction, not an answer. From past experience, I am assuming I will have to rewrite this in another form...perhaps by...
  45. O

    Laplace Transform Explained: WHY & HOW

    Laplace transform... I can't help but keep asserting how me textbook of differential equations just keeps stating new ideas without any background on WHY and HOW they were created. I've just started Laplace transform and the first thing i see is a blue DEFINITION box that just states the...
  46. C

    Inverse Laplace Transform Involving a Step (Heaviside) Function

    Hello, I have a fairly straight forward question regarding an inverse laplace transform. The function follows along with the solution. The solution (provided in my text) has been confirmed by Maple; however, i cannot account for the (1/3) in the solution. Any help would be greatly...
  47. E

    Laplace Transform of 5{\delta (t-3)}+4{u(t-2)}+3{e^{-5(t-3)}u(t-4)}

    Homework Statement Find the Laplace Transform of the following: 5{\delta (t-3)}+4{u(t-2)}+3{e^{-5(t-3)}u(t-4)} The Attempt at a Solution I know how to do the first and second terms, but I'm having trouble with the third. 5e^{-3t}+4\frac{1}{s}e^{-2t} + ? I think I should be using...
  48. L

    How Do I Find the Laplace Transform of an Integral?

    So I know the laplace transform of an integral is the product of the laplace transorm of the functions inside the integral, such as Laplace{integral from 0 to t [tau*e^(t - tau) d tau = Laplace[t] * Laplace[e^t], ignoring the tau what if I have Laplace{integral from 0 to t [t*e^(-tau) d tau]...
  49. J

    Finding the Laplace Transform for f(t)=2(1-u(t-1))+t(u(t-1))

    Homework Statement Given f(t)= 2 if 0<=t<1, and t if t>=1 I need to find the laplace transform. Homework Equations Using the second shifting theorem: f(t)= 2(1-u(t-1))+t(u(t-1)), which is the heaviside function. The Attempt at a Solution The first term, I understand. It is...
  50. G

    Laplace Transform: Answers for cos(4t-1)u(t-1) & cos4(t-1)u(t-1)

    what's the answer for laplace transform of the questions below? 1. cos(4t-1)u(t-1) 2. cos4(t-1)u(t-1) I want to compare the difference between these two answer. Thanks!
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