Okay this isn't really a problem, but I want it explained too me instead of the books way. We are doing a section on mechanical energy, and for the entire course with vectors, force, etc, we have always used rcostheta and rsintheto to find an x and y force. Now tell me why we do this? Is this to elimate the forces from a vector component form to a basic x y form, where y is a 90 degree value, and x is a 0 degree value? Also another question. We used the equation for change in mechanical energy where energy potential, and kinetic energy where the same regardless of its position along a path when looking at conservative forces. I used rcostheta and rsintheta to plug in values for velocity when they where at angles, but I noticed that this data does not accurately give the TOTAL potential energy correctly. To use an example say that a ball is fired at 600m/s at 30 degrees with a mass of 24kg. To plug this into the isloated system model for velocity I had to use velocity x sin30 but when it asked for its total mechanical energy at the balls maximum height I used 1/2mvf^2 and just plugged in 600.