Collision detection between a circle and rectangle

[Qobacha]

1) Rectangle or Square?
2) Are all Rectangles/Squares the same size?
3) Are the circles always the same size?

Hi,

Sorry for not making myself clear. Need to check the contact between the square(fixed size) and the circles(varying size) but i can make the circle fixed size if need be. I hope I'm clear. Thank you.