If you have that down, try another world (hint - it helps on higher levels to pick at least one spot where you know what the velocity is (zero?))
"AP" students - it's a good idea to use simulations (like the Universe Game) to mimic real world situations, or to use Logger Pro and the cart/ramp/motion detector setup to do the same
Let's try this out...

World 2-1 Example
This was done using a sky wifi livescribe pen - highly recommended! All the notes AND sounds are recorded and can be uploaded so you can share and save your classnotes :-)
Need more examples?
World 2-2
This was done using a sky wifi livescribe pen - highly recommended! All the notes AND sounds are recorded and can be uploaded so you can share and save your classnotes :-)
Need more examples?
World 2-2