A sphere of mass 2 kg and diameter of 10 cm is fired with the initial speed of 8 micrometres per second directly toward the center of a second sphere with mass of 500 kg and diameter of 1 m, which is held fixed. The spheres are initially a large distance apart, and at the end they hit each other. (a) What is the final gravitational potential energy of the system of two spheres (b) What work is done on the system by the gravitational force? (c) (Extra credit) Find the final speed of the small sphere.