Answer:
Both potential energy and kinetic energy are involved. As the book is falling, its potential energy decreases, and its kinetic energy increases.
Step-by-step explanation:
The potential energy depends on the height of the book, when the book decreases its height, the potential energy decreases.
The kinetic energy depends on the speed, when the book increases its speed, the kinetic energy increases.
Then, when the book is falling, the height is decreasing and the speed is increasing. It means that the potential energy is decreasing and the kinetic energy is increasing. So, the answer is:
Both potential energy and kinetic energy are involved. As the book is falling, its potential energy decreases, and its kinetic energy increases.