1. The problem statement, all variables and given/known data Hello everyone - here's my question: I am doing an assignment on projectile motion and I will be launching some balls from a compressor (that I have not seen yet!). I know how to calculate how much work will be done by the air expanding (will obv. depend on how much pressure is in the compressor); but i do not know how to go from there: do i say that the work done will equal the kinetic energy of the ball and just use the simple projectile motion formulae? If i do, isn't that neglectling the time taken for the ball to accelerate? If I take acceleration into account, i guess i would use momentum of air hitting ball = momentum of ball (elastic collision) then use f=ma on the ball. This will give me the acceleration of the ball. But how do I use the acceleration of the ball upwards with gravity taken into account? This would mean the acceleration would be highest at the launch, be 0 somewhere midair, decrease to 9.8 m/s then stay there? Perhaps there is an easy equation that I am forgetting (I would never rule that out!!!) 2. Relevant equations ummm.. thats what I am wondering.. if my first guess is right, then I use Ke= 1/2 m v2, if my second guess is right , then I use Newton's 3rd. 3. The attempt at a solution Please read part 1. Thanks for your help. P.S. If possible use metric units- I am Grade 11 Australia.