# particle with radius 'r' hits the plane. what is the point of contact?

A large particle with radius r hits the plane with perpendicular 'n' and passing through ,q'. I need to check whether it hits the plane or not. In order to do that I need to find the point of contact. My question is: we should shorten the 'p' by r to get the point of contact?

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@BadSniper: yes, you can add a length $r$ vector to the point $p$, oriented along the normal to the plane. The result is the same. – Ross Millikan Sep 17 '12 at 15:50
@BadSniper: that's why I said a length $r$ vector along the normal to the plane. If $\vec n$ is a unit normal to the plane, you have $p+r\vec n$ – Ross Millikan Sep 17 '12 at 19:52