Finding the total response of an undamped spring mass system

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Discussion Overview

The discussion revolves around finding the total response of an undamped spring-mass system, specifically focusing on the mathematical formulation of the system's response and the implications of initial conditions and external forces. The scope includes homework-related problem-solving and mathematical reasoning.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • The response of a spring-mass system is expressed as x(t) = (x0 - (F0 / (k - mω²))cos(ωnt) + (x'/ωn)sin(ωnt) + (F0 / (k - mω²))cos(ωt), with various parameters defined.
  • One participant suggests that F0 and ω cannot be solved for as they are arbitrarily supplied by an external agency.
  • Another participant questions the possibility of substituting the given f(t) with that for harmonic motion, noting the challenge of having one equation with two unknowns.
  • A further contribution points out the presence of three terms in the relevant equation and asks which could be affected by gravity alone, considering the initial conditions are zero.

Areas of Agreement / Disagreement

Participants express disagreement regarding the solvability of F0 and ω, with some asserting they cannot be determined while others explore the potential for substitution methods. The discussion remains unresolved as to the implications of gravity on the terms of the equation.

Contextual Notes

There are limitations regarding the assumptions made about the external forces and the initial conditions, which may affect the analysis of the system's response.

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Homework Statement


spring mass system.JPG


Homework Equations


The response of a spring mass system can be simplified to equal:
x(t) = (x0 - (F0 / (k - mω2))cos(ωnt) + (x'/ωn)sin(ωnt) + (F0 / (k - mω2))cos(ωt)

where
x & x' are the initial conditions
ω is the exciting frequency
ωn is the natural frequency
k is the spring constant
m is the mass
and F0 is the amplification of the applied force

ωn = √(k/m)

The Attempt at a Solution


Given normal initial conditions, x = x' = 0

x(t) = - (F0 / (k - mω2))cos(ωnt) + (F0 / (k - mω2))cos(ωt)

and ωn = √(k/m) = 6.325rad / s
Is there a way to solve for F0 and ω?
 
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No. Those are arbitrarily supplied by an external agency.
 
Simon Bridge said:
No. Those are arbitrarily supplied by an external agency.
That's what I thought but someone said you could by substituting the given f (t) with the f (t) for harmonic motion - but it seemed like I still on had one one equation 2 unknowns so it didn't seem possible.
 
There are three terms in your "relevant equation". Which one or ones look like they could be affected by gravity alone? Remember initial conditions = 0.
 

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