What went wrong with my solution for a damped mass spring system?

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Discussion Overview

The discussion revolves around solving a second-order linear differential equation representing a damped mass-spring system. Participants explore the general solution and initial conditions, seeking to identify errors in the calculations and reasoning involved in deriving the solution.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Homework-related

Main Points Raised

  • One participant presents the differential equation x'' + 10x' + 64x = 0 and their derived general solution, expressing confusion over a subsequent calculation.
  • Another participant suggests that a term may have been omitted in the calculations, specifically mentioning the coefficient 6.245.
  • A further response elaborates on the calculations for the initial conditions, providing a breakdown of how to find the coefficients c1 and c2 based on the initial values given.
  • One participant indicates that they were able to correct their solution after following the provided guidelines and recalculating.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the initial confusion, but there is a collaborative effort to clarify the calculations and correct the approach. The discussion includes multiple viewpoints on the solution process and the handling of coefficients.

Contextual Notes

There are unresolved aspects regarding the specific calculations and the handling of the coefficients, as well as the potential omission of terms in the solution process.

FHamster
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So the equation is x'' + 10x' + 64x = 0
x(0) = 1
x'(0) = 0
I get general solution of e^(-5t)(c1*cos(6.245t) + c2sin(6.245t) )
From there I get e^(-5t)cos(6.245t)+5e^(-5t)sin(6.245t)
but it wrong. What the gerbils am I doing wrong?

Thanks
 
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Welcome to PF!

Hi FHamster! Welcome to PF! :smile:

(try using the X2 button just above the Reply box :wink:)
FHamster said:
So the equation is x'' + 10x' + 64x = 0
x(0) = 1
x'(0) = 0

From there I get e^(-5t)cos(6.245t)+5e^(-5t)sin(6.245t)
but it wrong. What the gerbils am I doing wrong?

(do hamsters not like gerbils? :biggrin:)

erm :redface: … haven't you left out a 6.245 ? :wink:
 
FHamster said:
So the equation is x'' + 10x' + 64x = 0
x(0) = 1
x'(0) = 0
I get general solution of e^(-5t)(c1*cos(6.245t) + c2sin(6.245t) )
From there I get e^(-5t)cos(6.245t)+5e^(-5t)sin(6.245t)
but it wrong. What the gerbils am I doing wrong?

Thanks
If [itex]y= e^{5t}(c_1cos(6.245t)+ c_2sin(6.245t))[/itex]
then [itex]y(0)= e^0 (c_1 cos(0)+ c_2 sin(0))= c_1= 1[/itex] so you have that coefficient right.

[tex]y'= 5e^{5t}(c_1 cos(6.245t)+ c_2 sin(6.245t))+ e^{5t}(-6.245 sin(6.245 t)+6.245cos(6.245t))[/tex]

[tex]y'(0)= 5e^0(c_1 cos(0)+ c_2 sin(0))+ e^0(-6.245c_1 sin(0)+ 6.245c_2 cos(0))[/tex]
[tex]y'(0)= 5(c_1)+ (1)(6.245c_2)= 11.245[/tex]
Knowing that [itex]c_1= 1[/itex], solve for [itex]c_2[/itex].
 


Thanks, following some of these guidelines and doing some recalcumacations. I managed to get it right

tiny-tim said:
Hi FHamster! Welcome to PF! :smile:

(try using the X2 button just above the Reply box :wink:)


(do hamsters not like gerbils? :biggrin:)

erm :redface: … haven't you left out a 6.245 ? :wink:



Hamsters are the masterrace.
 

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