There is no way to find the force between two objects (when they collide with each other) without further information.
e.g. model for interaction between object when they collide.
You are welcomed to check out [url=http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=193.0]Simulate 1D collision with a virtual spring[/url]. A spring is used to model the collision process(spring constant depends on the softness of both objects).