Can 2d physics be used to influence a UI slider?

It could but doesn't sound like a good use-case. For starters, it means your UI has to be in world-space which isn't common as it's typically in camera/screen-space.

From your other post, it seems like you're simply after some physical behaviour like drag. Adding those things is much easier to do yourself via a simple script rather than trying to bind a rigidbody physics simulation to a UI.

 

You'd have to write it yourself depending on what motion you want. There are various examples of dynamic UI around the web. Here's one that might have something you need: https://github.com/desandro/practical-ui-physics.