Find Y(s) and y(t) by laplace transform.

evrimesa

evrimesa

Answered question

2021-12-07

Take the Laplace transform of the following initial value and solve for Y(s)=L{y(t)}:

              sin(π t), 0 ≤ t <1

y''+9y= {                               y(0)=0, y′(0)=0

                  0, 1 ≤ t

a) Y(s)= ? (Hint: write the right hand side in terms of the Heaviside function)

b) Now find the inverse transform to find y(t)= ? . (Use step(t-c) for uc(t) .)

Note= π/ (s^2+π^2)(s^2+9) = π/ π^2 -9 (1/(s^2+9) - 1/(s^2+ π^2)

Answer & Explanation

star233

star233

Skilled2023-04-21Added 403 answers

We want to find the Laplace transform of the given function y(t)=sin(πt) for 0t<1, and solve for Y(s)=L{y(t)}.

The Laplace transform of y(t) is defined as:

L{y(t)}=[0,)e-sty(t)dt

Substituting y(t)=sin(πt) and integrating over the given interval [0,1], we get:

L{y(t)}=[0,1]e-stsin(πt)dt

Using the identity sin(a)=eia-e-ia2i, we can rewrite the above expression as:

L{y(t)}=(12i)[0,1](eiπte-st-e-iπte-st)dt

We can evaluate these integrals using the formula eatdt=(1a)eat. This gives:

L{y(t)}=(12i)[(1s-iπ)-(1s+iπ)]

Simplifying the above expression, we get:

L{y(t)}=(πs2+π2)

Now, we need to solve the differential equation y''+9y=0 with initial conditions y(0) = 0 and y'(0) = 0, using the Laplace transform.

Taking the Laplace transform of both sides of the differential equation, we get:

s2Y(s)-sy(0)-y'(0)+9Y(s)=0

Substituting y(0) = 0 and y'(0) = 0, we get:

s2Y(s)+9Y(s)=0

Factoring out Y(s), we get:

Y(s) (s^2 + 9) = 0

Therefore, the Laplace transform of the solution y(t) is:

Y(s) = 0, if s±3i

Now, we need to find the inverse Laplace transform of Y(s) to get the solution y(t). Using the formula for inverse Laplace transform, we get:

y(t)=(12πi)[c-i,c+i]estY(s)ds

where c is a constant such that the line Re(s) = c is to the right of all singularities of Y(s).

In this case, the only singularity of Y(s) is at s = ±3i, so we can choose c > 3.

Using the residue theorem, we can evaluate the above integral as:

y(t)=(1π)Res(estY(s),sj)

where the sum is taken over all singularities sj of Y(s) in the region Re(s) > c.

In this case, the only singularity is at s = 3i, and its residue is:

Res(estY(s),s=3i)=lims3i(s-3i)estY(s)=(3i2π)e3it

Therefore, the solution to the differential equation with initial conditions y(0) = 0 and y'(0) = 0

Do you have a similar question?

Recalculate according to your conditions!

New Questions in Differential Equations

Ask your question.
Get an expert answer.

Let our experts help you. Answer in as fast as 15 minutes.

Didn't find what you were looking for?