Dynamic Analysis - What will be the amplitude

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[radou]

A disturbing force of 9N acts harmonically

I assume this means that the force is given with 9*sin(ωt), where ω is one of the given frequencies?

 

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[radou]

Here, this should help, it's a solution for undamped oscillations with an harmonic excitation:

http://www.fs.cvut.cz/en/U2052/node116.html

The amplitude is different, as you can see.