Forced oscilation/position

  • Thread starter qasbrv
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  • #1
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Homework Statement
A spring is stretched 2m by a mass of 2 kg. The body is immersed in a viscous fluid with the damping coefficient having 4 Ns / m which is driven by an external force 4cos (2t). Plot mass position versus time. g = 10 m / s2.

The attempt at a solution
I know first I have to find an equivalent form as that of forced oscilations
x⋅⋅+2γx02x = F×cos(ωt)/m
but I can't figure out because I don't have an elasticity const k or a frequency. I think I don't need one, but I don't know how to start.
 

Answers and Replies

  • #2
Simon Bridge
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Don't you need the spring constant to find the natural frequency?
Is there any other information supplied? Maybe in the context?
 
  • #3
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Don't you need the spring constant to find the natural frequency?
Is there any other information supplied? Maybe in the context?
I thought that too, but that's all; nothing else given. Maybe the problem has some bugs.
 
  • #4
Simon Bridge
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Maybe ... ask.
 
  • #5
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I will
Thank you anyway!
 
  • #6
vela
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What do you suppose "a spring is stretched 2m by a mass of 2 kg" means?
 
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  • #7
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It means that the maximum elongation x (amplitude) is exerted by the gravitational force =m*g ...so
-m*g=-kx
k=m*g/x= 10 N/m xD

Thank you very much!
 
  • #8
Simon Bridge
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Ooh... I missed it too, well done.
 
  • #9
rude man
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Poorly worded problem.
Is the mass subjected to the force 4cos (2t) directly, or is the force exerted on the mass indirectly by applying the force to a container containing the mass and viscous fluid? If the latter the mass of the fluid + containing vessel would also have to be specified.
 

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