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leonidas24
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Homework Statement
A block of mass m moves on a horizontal, frictionless table. It is connected to the centre of the table by a massless spring, which exerts a restoring force F obeying a nonlinear version of Hooke's law,
[tex]F = -kr + ar^3[/tex]
where r is the length of the spring. Show that the maximum energy for which the block remains bound to the centre of the table is approximately
[tex]E \approx \frac{k^2}{4a}[/tex]
if a is small and positive. Draw a diagram to support your answer.
Homework Equations
Lagrangian:
[tex]L = \frac{1}{2}m(\dot{r}^2 + r^2\dot{\phi}^2) - \frac{kr^2}{2} + \frac{ar^4}{4}[/tex]
Energy for radial coordinate:
[tex]E = \frac{m\dot{r}^2}{2}+ \frac{J^2}{2mr^2}+ \frac{kr^2}{2} - \frac{ar^4}{4}[/tex]
Energy and angular momentum [tex]J[/tex] are contants of motion.
The Attempt at a Solution
I'm really not sure how to tackle this one. Just a nudge in the right direction is all I'm after.
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