Answer:
Correct answer letter b.
Explanation:
When the book is on the top shelf of the bookcase, it just only gravitational potential energy, due to the gravitational field and the kinetic energy at this point is zero because the book is at rest.
Now, when the book starts falling, all the potential energy will transform into the kinetic energy. It happens, thanks to the conservation of the energy,that says energy can neither be created nor destroyed, energy can only be transferred or changed from one form to another.
Let's recall that the gravitational potential energy depends on the object's position, so when the book falls, the magnitude of the position decreases and the speed of this object increases.
Therefore, the potential energy of the book decreases as kinetic energy increases.
Correct answer letter b.
I hope it helps you!
