Question 16

Unfortunately, I don't think I will be able to contribute much to this discussion.  This is my first course in mechanics, and I have yet to refer to a textbook.  In related fields, such as differential equations, I also have not found a textbook that is more useful to me than internet resources.  My favorite spots online are Eric Weisstein's World of Physics and the related site Wolfram MathWorld.  Both of these websites provide a trusted, instantly accessible reference on a broad range of topics in physics and mathematics.   If anyone has not discovered these resources, I would suggest that they take a look. 

I am finding others' suggestions on textbooks very helpful, however.