We consider a common due-date assignment and single machine scheduling problem in which job processing time has position-dependent workload. Assume that the processing time of a job is a convex function of the amount of a resource allocated to it, its position in the processing sequence and workload. All jobs have a common due date. The objective is to find the optimal due date, the optimal resource allocation scheme and the optimal job sequence so as to minimize the total cost, which is a function of earliness, tardiness, due-date, resource consumption. We introduce an efficient O(n3)algorithm to solve the problem.