A 1.4 kg book is lying on a 0.80m -high table. You pick it up and place it on a bookshelf 2.1 m above the floo

Question

A 1.4 kg book is lying on a 0.80m -high table. You pick it up and place it on a bookshelf 2.1 m above the floor.

How much work does gravity do on the book?

Express your answer using two significant figures.

How much work does your hand do on the book?

Express your answer using two significant figures.

Answer 1

The amount of potential energy of an object that is raised a height h is

E=mgh.

The book is raised h=2.1-0.8=1.3 m

The work done is

E=mgh=1.4*9.81*1.3=17.85 J

The amount of work done on the book by gravity is the opposite of the work done by your hand.

Egrav = -Ehand = -17.85 J