General Energy conservation question

[Rock32]

This isn't really a homework question, so I'm hoping I can just get a straight answer from someone (although it is related to questions).

I realize that you can choose U = 0 anywhere you want in a gravity-related problem, ideally choosing a place where it is easiest to manipulate mgy values.

However, in a problem where both a spring force and gravity are of concern (i.e. where a spring is at an angle or hanging vertically), can you choose two different U = 0 positions?

That is, can you choose the lowest point to be Ugrav = 0 and the point where the spring is relaxed to be Uspring = 0, even if the two places are not the same y value? Or, do both PE's have to align?

Thanks.

 

[Delphi51]

Yes, choose the spring U to be zero when relaxed and the gravitational energy zero height entirely separately.

 

[kerimek]

I can provide a response to your question. In general, the choice of U = 0 for potential energy depends on the reference point you choose for your system. In a problem involving both a spring force and gravity, you can choose two different U = 0 positions as long as you are consistent with your reference point throughout the problem. This means that both potential energies (gravitational and spring) will have different values at different points in the system, but their relative difference will remain the same. So, in short, you can choose different U = 0 positions for both gravitational and spring potential energies as long as you are consistent with your reference point throughout the problem. I hope this helps.