I would be very careful with this because it is very hard to get velocity with acceleration from something like the built in accelerometer. Our team has messed with it alot and found there is no good way to figure it our because you have a LOT of noise comming from it. The only real use we found is just telling which direction the robot is going.
The earth has a huge force that is hard to get rid of. If you want to get something accurate enough to tell velocity you might want to go get the NavX board sold my andymark but even with that board the velocity is only accurate for only about 2-3 seconds before it starts to get off.
If the accelerometer was accurate enough to tell speed we would have used them in cars on such. But because of the earth it won't be useful as you think it would. What you learn in physics is only ideal situation.
