Spring connect two objects in graviy field

[Fu-Kwun Hwang]

Two objects with mass m₁ and m₂, connected with a spring (spring constant k).
You can drag the top one and compress it.
What is the minimum force (Fext) to bring the mass m₁ jump up?
You can drag Fext to compress the spring,too!

If L0 is the original length of the spring.
The equilibrium poisition y₁=y₂+L0-m₁*g/k;
F1=m(d²y₁/dy₁²)= -k*(y1-y2-L0)-b*vy₁;

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<applet code='users.ntnu.fkh.mass2spring_pkg.mass2springApplet.class' archive='http://www.phy.ntnu.edu.tw/ntnujava/ejsuser/2/ejs_mass2spring.jar' name='mass2spring4103' id='mass2spring4103' width='800' height='400' mayscript=true><param name='draggable' value='true'></applet>
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