I'm REALLY hoping you can help me here!

I've been asked to produce the following using vPython, if you could help me setup a model, or even create one in java, I can then quite easily convert it to python.
I just need to have the basic physics explained to me... I've attempted it myself but I really can't get my head around it!!!!
here goes:
[quote]A mass of 2 kg is dropped vertically into a frictionless slide located in the x-y plane. The mass enters with zero velocity at (-5,5) and exits travelling horizontally at (0,0).
Assuming the slide to be perfectly circular in shape construct a model of the forces acting on the mass and hence simulate its motion. [/quote]

So, it's a quarter-circle starting at (-5,5), ending at (0,0) with centre (0,5) i.e.
Initial velocity is (0,0), initial position is (-5,5), initial acceleration is (0,-g) ( where g is 9.81ms^2)

I have attempted to draw force lines and things but ... agggh!! Variable acceleration!!!!!
I can't handle it,

Please can you help me !! :)