پاسخ : حرکت
dx=kdt
az tarafi bar asase moadeleye dayere darim y=(r^2-x^2)^1/2
ba moshtaghgiri darim
dy=
kholase hosele nadaram be englisi benevisam khodetun hal konin kholase difransiel harkat ke sorat bashe be dast miad aslan ham lazem nist inghad khodetuno be zah mat bendazin(az fisaghores hesab mishe difransiel harkat yani dx^2+dy^2)