A toy cannon uses a spring to project a 5.39 g soft rubber ball. The spring is originally compressed by 4.99 cm and has a force constant of 8.04 N/m. When the cannon is fired, the ball moves 15.8 cm through the horizontal barrel of the cannon, and there is a constant frictional force of 0.0328 N between the barrel and the ball. At what point does the ball have maximum speed? I do not know where to start... If I set F=fx and F=ma, then I get speed at 4.99cm which is incorrect. Can someone please help?