you place a book on top of a spring and push down, compressing the spring by 10 cm. when you let go of the book, it is pushed up by the spring. which statement describes what happens to the energy of the spring-book system?

a. the elastic potential energy of the system decreases.
b. the gravitational potential energy of the system decreases.
c. the kinetic energy of the system decreases.
d. the total energy of the system increases.