Q:

Sign conventions

I had my first class of Applied Physics for Electrical engineering. And I am stuck in something very basic. The sign conventions. They are pretty confusing. The teacher said the position of origin din't matter. But some basic calculation I ran oppose that idea. I am attaching a picture. Please do tell me if something is technically wrong or am I too dumb?

A:

The displacement in your first example should be negative, since you took origin to be above the final point and the acceleration to be negative going downwards.

