## Lagrangians and P-Conservation

I have a problem with a particle experiencing a central force towards some origin, as well as a gravitational force downwards. I've calculated the Lagrangian, and the equations of motion. Now I'm being asked to see if the system follows conservation of angular momentum. How do I do this? I know it has something to do with seeing if the system is invariant of rotation, but how do I check for that?

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 If $$\frac{\partial L}{\partial q} =0$$ then the conjugate momentum $$\frac{\partial L}{\partial \dot{q}}$$ is a conserved quantity. If that doesn't clear things up, then post what you have for the Lagrangian.
 But the conjugate momentum is the same as the angular momentum only in some cases. Compute H and chech if H commutes with J.