This is nothing but a poor attempt to rationalize what you know to be in stark contrast with your principles/morals. If you were a true environmentalist, as you say, the thought of majoring in petroleum engineering would disgust you.
To answer your question, don't major in either.
I would recommend not using Strang's Intro to Linear Algebra. I did not like that book at all. It was much too informal/conversational for my tastes. Perhaps you like that style though?
To provide a counter-example for the OP, in my general physics 1 class there were no "plug and chug" worksheets as Chunkysalsa describes. We were usually assigned about 15 problems per week out of the textbook (Physics by Giambattista).
It helps to take algebra/trig physics beforehand (if you've got the time for it). I say this because you're basically going through the same material again, just at a deeper level. I took general physics 1 last summer and now I'm taking calc-physics 1. I recognize/remember a lot of the...
As my physics professor tells me:
1. make a sketch of the problem
2. write down the variables (both known and unknown)
3. write down the concept (for example f=ma etc etc)
4. write down the working equation/s
5. solve the problem
I would talk about certain things that I would want to accomplish at said university, which professor/s I would hope to do research with and specifically what kind of research. Perhaps there are some clubs/organizations that are related to your major that you would want to get involved in as well.
Most of the first-year physics courses for engineering students would use something like University Physics by Young and Freedman. You could also try An Intro to Mechanics by Kleppner and Kolenkow.