A spring has an unstretched length of 12 cm. When an 80 g ball is hung from it, the length increases by 4.0 cm. Then the ball is pulled down another 4.0 cm and released. 

a. What is the spring constant of the spring? 

b. What is the period of the oscillation? 

c. Draw a position-versus-time graph showing the motion of the ball for three cycles of the oscillation. Let the equilibrium position of the ball be y = 0. Be sure to include appropriate units on the axes so that the period and the amplitude of the motion can be determined from your graph.