# Incline newton's 3rd law

1. Nov 10, 2008

### steve0827

1. The problem statement, all variables and given/known data
a book restson the shelf of a bookcase. the reaction force to the force of gravity acting on the book is?
A.)the weight of the book
B.)none of these
C.)the force of the shelf holding the book up
D.)the frictional force between the book and shelf
E.)the force exerted by the book on the earth

2. Relevant equations
N/A

3. The attempt at a solution
I thought the answer was C...but i was wrong.

i really need help on this

2. Nov 10, 2008

### marlon

First question : how would you calculate the reaction force ? Imagine the book has a certain mass equal to 1 kg or whatever.

Draw a free body diagram and apply Newton's second law.

marlon

3. Nov 10, 2008

### steve0827

i think its either A or B
could you give me a hint if those are right :P

4. Nov 10, 2008

### marlon

Why do you think it's A or B ?

marlon

5. Nov 11, 2008

### Staff: Mentor

Note that "reaction force" here is used in the Newton's 3rd law sense of "action/reaction".

Hint: What two bodies are involved in this interaction?

What does Newton's 3rd law say when two bodies interact?