Answer
See explanation.
Work Step by Step
a. When the displacement is upward, the gravitational force is downward, so gravity does negative work. The gravitational potential energy of the book increases – it has more PE when it is higher up.
b. When the displacement is downward, the gravitational force is downward, so gravity does positive work. The gravitational potential energy of the can decreases – it has less PE when it is lower down.
