# Forced oscilation/position

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.

Simon Bridge
Homework Helper
Don't you need the spring constant to find the natural frequency?
Is there any other information supplied? Maybe in the context?

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.

Simon Bridge
Homework Helper

I will
Thank you anyway!

vela
Staff Emeritus
Homework Helper
What do you suppose "a spring is stretched 2m by a mass of 2 kg" means?

• Simon Bridge and qasbrv
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!

Simon Bridge