I'm not sure wether I understand this part of the exercise. In BouncingBall class I added a new methode for kinetic energy (I initialized the variables)
public void calc(){
energy = ((vx*vx)+(vy*vy)/2);

and in the App Class in doStep
for (int i=0;iball[i].calc();
totalenergy +=ball[i].energy ;
}
control.println("totalenergy = " +totalenergy);

It works well, however the results seem to be strange When I plot the result I get an up and down curve for each ball. With large number of balls the plot is almost completely full. When I add the potential energy as well (y*g) I get a streigth line upwartds. Can you comment my code and the result? Did I missunderstand the exercies?
So far all exercises in Chap 2 have not been a problem.
regards

martin

Post edited August 2, 2012 at 11:23 AM EST.