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Conference rusure::math

Title:Mathematics at DEC
Moderator:RUSURE::EDP
Created:Mon Feb 03 1986
Last Modified:Fri Jun 06 1997
Last Successful Update:Fri Jun 06 1997
Number of topics:2083
Total number of notes:14613

1356.0. "laplace problem help" by DCSVAX::MOORADIAN () Thu Dec 13 1990 08:40

    Need help on the following problem:
    
    	A system is described by the eqn
    
    	(d**2)y/d(t**2) + 3 (dy/dt) + 2y = dx/dt + 3x
    
    	where x(t) = 10 u(t) Volts is the input  and
    	      y(t) is the output
    
    	y(t) must be found using Laplace transforms
    Thanks
    -----------------------------------------------------------------
    	
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1356.1HPSTEK::XIAIn my beginning is my end.Thu Dec 13 1990 14:0115
    Take Laplace transform, you get:
     2
    s Y(s) + 3sY(s) + 2Y(s) = 10sU(s) + 3U(s)
    
    Then you get:
    
            (10s + 3)
    Y(s) = ------------ U(s)
            (s+1)(s+2)
    
    Now you got to tell us what u(t) is and then, hopefully, you can figure
    out what U(s) is, then it becomes a matter of splitting the rational
    and take the inverse Laplace transform.
    
    Eugene
1356.2ALLVAX::JROTHSaturday alley up to Sunday streetThu Dec 13 1990 17:3314
         <<< Note 1356.1 by HPSTEK::XIA "In my beginning is my end." >>>

>    Now you got to tell us what u(t) is and then, hopefully, you can figure
     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>    out what U(s) is, then it becomes a matter of splitting the rational
>    and take the inverse Laplace transform.

    I see you're not an engineer :-)

    u(t) is the unit step function most likely.  Note that you have to
    specify the initial conditions on y(t) to make a unique solution.
    Beyond that, it's a plug-in homework problem.

    - Jim
1356.3HPSTEK::XIAIn my beginning is my end.Fri Dec 14 1990 13:007
    Uh... Jim,  I have a B.S. degree in EE.  :-)  In control classes (where
    most of those things come up), u(t) usually stands for some arbitrary
    linear input (ok, maybe my memory is a bit rusted).  You are right, we
    need to know y(0).  In my solution, I just assumed that y(0)=0, and it
    is a standard "plug&chug" homework problem.
    
    Eugene
1356.4check out the Schaums Outline for more helpALLVAX::JROTHSaturday alley up to Sunday streetFri Dec 14 1990 15:0817
         <<< Note 1356.3 by HPSTEK::XIA "In my beginning is my end." >>>

>    Uh... Jim,  I have a B.S. degree in EE.  :-)  In control classes (where

   Hah!  You could have fooled me, you've used some mathematics-sect
   jargon at times that no engineer would be caught dead using :-)

   Re .0

   There's an inexpensive Schaums outline on the Laplace Transform that
   I recommend - you might want to check it out to supplement your course.
   It will really clarify the ideas.

   [For introductory math many of the outlines are really excellent - can
    hardly beat the prices either!]

   - Jim