Physics

Gravitational potential energy measures how much energy an object stores by virtue of its height. The key insight is that only the change in height matters—not the absolute position—so you'll find $\Delta h$ and multiply by both mass and gravity using $\Delta PE = mg\Delta h$. This tells you how much energy the Earth-book system gained when the book was lifted.

Gravitational potential energy measures how much energy an object stores by virtue of its height. The key insight is that only the change in height matters—not the absolute position—so you'll find $\Delta h$ and multiply by both mass and gravity using $\Delta PE = mg\Delta h$. This tells you how much energy the Earth-book system gained when the book was lifted.