on 04-08-2018 06:44 AM
More of a discussion response than a direct answer, but the key to deter students copying is providing unique questions/assessments. Most online homework platform's assignment editing options allow for you to change settings such to randomize, shuffle or pool questions within an assignment. Other options may be available at the question level to enable randomization of variable/answers. Finally, consider modifying an existing question or self-authoring your own question.
Working with other instructors, many will set a time limit on the assignment if the option is available and/or make the students complete the assignment in class if taught face-to-face.
While I do not cover math and science based disciplines, it looks like WebAssign is Cengage's core digital platform for Physics titles. You can find a variety resource materials at https://www.cengage.com/training/webassign
Specifically, check out Section 8, Configuring Question Behavior, in the Comprehensive Instructor Guide to Creating Questions in WebAssign - https://embed.widencdn.net/pdf/plus/cengage/p9ehhfenht/gui_EWA-create-questions-guide.pdf?u=c8lcjz
This has a section on Randomizing Question Values (starts at page 252) and provides not only reasons why to randomize, but also best practices and other considerations when doing so.
Hope this helps