How should I inverse Laplace transform this function? ((omega_n)^2)/(s^2+bs+c)

limfne2c

limfne2c

Answered question

2022-10-17

How should I inverse Laplace transform this function?
( ω n ) 2 s 2 + b s + c

Answer & Explanation

espava8b

espava8b

Beginner2022-10-18Added 12 answers

In such a case the most convenient way to compute the inverse transform is to use standard results from Laplace transform tables. The transform pairs that you need here can be found in most tables:
1 s 2 t u ( t ) ω 0 s 2 + ω 0 2 sin ( ω 0 t ) u ( t ) ω 0 s 2 ω 0 2 sinh ( ω 0 t ) u ( t ) f ( t ) F ( s ) e α t f ( t ) F ( s + α )
Now rewrite the function as
X ( s ) = ω n 2 s 2 + b s + c = ω n 2 ( s + b / 2 ) 2 + c b 2 / 4
You have to distinguish 3 cases:
c > b 2 / 4: Define ω 0 2 = c b 2 / 4
X ( s ) = ω n 2 ω 0 ω 0 ( s + b / 2 ) 2 + ω 0 2 ω n 2 ω 0 e b t / 2 sin ( ω 0 t ) u ( t )
c < b 2 / 4: Define ω 0 2 = b 2 / 4 c
X ( s ) = ω n 2 ω 0 ω 0 ( s + b / 2 ) 2 ω 0 2 ω n 2 ω 0 e b t / 2 sinh ( ω 0 t ) u ( t )
c = b 2 / 4
X ( s ) = ω n 2 1 ( s + b / 2 ) 2 ω n 2 e b t / 2 t u ( t )

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