A Hint on Learning Physics
You cannot learn physics just by memorizing formulas - you must also learn their meanings! (Of course, you may also have to memorize a few formulas, but there is an easier way to do this.)
Every equation is a summary of an idea. Each symbol in an equation represents something. The equation itself expresses a relationship between these things. You have to know the meaning of every symbol and the relationships expressed by the equation, and then you will know the idea. To learn physics you must know the idea.
Just picking out an equation from a list, or from memory, and then plugging in values, is not enough. You have to know what it all means. Compare this to balancing your checkbook: You may know how to add and subtract, but the arithmetic is only a tool for getting the final answer (your account balance). You also have to know which items are deposits and which items represent checks, (this is like knowing the meaning of the symbols in an equation), and you have to know that you add deposits and subtract checks (this is analogous to knowing the relationship between the symbols).
This may sound like extra work, but it actually can make your job easier. Once you know the idea expressed by an equation it is easier to remember that equation, and easier to know what to do with it.
Try to think of it this way:
Put the Principle first -- the equation comes last.