1. The problem statement, all variables and given/known data A uniform sphere of radius R is cut into two portions. The smaller portion S has height h measured from its flat surface, where h<R. (a) Locate the center of mass of S from its flat surface (b) Use (a) the locate the centre of mass of a hollow H which has the same shape and same size as S. The hollow has only a thin curved surface and without any flat surface. (c) Obtain the result of (b) by direct integration. 2. Relevant equations This question use 2 tricks to find the center of mass of a hollow. 1. Use substraction to substract a big object by a smaller one and then take limit. (I hope you understand what I mean.) 2. Use direction integration. 3. The attempt at a solution My answer in part b doesn't agree with part c, can anyone help me to check what happen?