1. The problem statement, all variables and given/known data We have got a ball of radius r, which is falling from the roof of the house. How is the radius r with respect to time? We are looking at the ball directly from above and ball is at the beginning of fall x from our eyes. Neglect air resistance. 2. Relevant equations I'm not sure what to write here. So I think the nub is equation of free fall: s= 1/2gt^2 radius decreases quadratically 3. The attempt at a solution So, I know equation: s= 1/2gt^2 I think the radius decreases quadratically, because t^2. I must attributed the x (s from eyes before free fall) And my equation: r(t)= r/(1/2gt^2 + x) It is right? Thanks for help. PS: Sorry for bad English, but I don't know better yet.