During their first physics courses, most students struggle with mathematical concepts that are used but not fully understood, for example, the appearance of infinity in introductory physics exercises. In many cases, these concepts are critical to understanding the underlying physical phenomenon. Typically, most books do not place much emphasis on this type of analysis, which we believe is essential for the training of physics students. In this article, we will try to fill that gap by discussing three exercises that are frequently studied in introductory physics courses where objects of infinite length are involved. In this work, we find that it is possible to determine the length of an object that for practical purposes behaves like an object of infinite length.