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Forced oscilation/position

  1. Jun 16, 2016 #1
    The problem statement, all variables and given/known data
    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.
     
  2. jcsd
  3. Jun 16, 2016 #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?
     
  4. Jun 16, 2016 #3
    I thought that too, but that's all; nothing else given. Maybe the problem has some bugs.
     
  5. Jun 16, 2016 #4

    Simon Bridge

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    Maybe ... ask.
     
  6. Jun 16, 2016 #5
    I will
    Thank you anyway!
     
  7. Jun 16, 2016 #6

    vela

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    What do you suppose "a spring is stretched 2m by a mass of 2 kg" means?
     
  8. Jun 17, 2016 #7
    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!
     
  9. Jun 17, 2016 #8

    Simon Bridge

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    Ooh... I missed it too, well done.
     
  10. Jun 18, 2016 #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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