(Projectile Motion)How to derive the equation?? I made a device which use elastic band to launch a ping pong ball. I have measured the distance travelled with different length of stretch at constant 36 degree launch angle. The graph plotted out is kind of curved, not straight line. And now I am asked to derive an equation to determine distance as a function of stretch.... Does anyone know how to do this? Cuz I spent almost a day still duno how to do it.