# What do you see in this diagram?

## Homework Statement

In this problem i'm asked to give the differential equation of the mechanical system in the following diagram:

http://www.jelp.org/imagenes/mech.jpg

## Homework Equations

Once i understand the diagram, i'll get the motion equation by newton or lagrange. But what is G in the diagram?? I can't ask to the "creator of the draw". Is the black dot fixed? What do you think?? Thanks a lot...

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