My sphere has density, $p(R)=(R+10)^-2$. If I collapse this sphere into a $2D$ plane, let's say it forms a $2D$ ellipse as a result, how will I calculate the mass of this $2D$ ellipse? in what possible ways can we interpret this? Perhaps mass of ellipse=density $x$ area of ellipse, in a rough manner?
any logical answer is welcome, I want to know your thoughts. Please give some basic calculations to aid your thought if possible. thanks.