Calculate shadow path&size + object size based on distance

What are the variables I need to take in account if I want to calculate shadow path and size?
I will try to simplify my questions.

I have a $2D$ circle (radius: $28$) which means the size of the circle (in box) is $56\times 56$ at specific point (lets say $(300,300)$).

I tell the $2D$ circle to go in specific path, lets say from ($300,300$) to ($300,200$).

I want to tell its shadow what path to do based on the $2D$ circle path.
ofcourse the size of the ball need to be calculated aswell..
I guess I need some extra variables because I am talking about $3D$ space in $2D$.. (lets say the "sun" is always above the ball so you don't need to calculate its degrees from the "sun", only its distance)

I am pretty sure it's possible but I have no idea how to calculate and what extra variables I need...

Basically, something like that: http://jonobr1.github.io/Physics/examples/cloth.html

Hopefully you understood what I want, if u didnt just tell me which part and I will try to re-explain or something.
Thanks

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