Use the free drafting program Xcircuit.
Xcircuit is a simple yet powerful 2-D CAD program is specifically designed to draw electrical schematics, but it works well for many applications. Best of all, its native output format is Encapsulated PostScript (.eps), which is exactly what TeX needs for its embedded graphic images.
The only disadvantage to using Xcircuit is that it is designed to run on Linux computers. I've been told that running it on a Microsoft Windows computer is possible, but complicated.
You may obtain Xcircuit by downloading it from one of a few sites on the internet. Just use "Google" for directions.
Yes, you may use other software to create graphic files for inclusion into worksheet problems, but the graphic file format must be Encapsulated Postscript (.eps) in order to be accepted by the "TeX" typesetting software used to compile the worksheets. Thus, it makes sense to use a drawing/drafting program whose native output is Encapsulated PostScript, if possible. The alternative -- to use other software packages to create non-EPS images and then convert the image format to EPS -- may result in very large graphics files, and/or images that appear "fuzzy" in the final document.