5. Force on a curved surface A body is subject to a state of nominal stress s in the current state. Consider a set of material particles. When the body is in the reference state, the set of material particles forms a three- dimensional region bounded by two surfaces. One surface is flat, of area A and unit normal vector N. The other surface is curved. Calculate the total force acting on the curved surface. (Hint: force needs to be balanced for any volume of materials)