Three books (X, Y, and Z) rest on a table. The weight of each book is indicated. The net force acting on book Y is:
A) 4 N down
B) 5 N up
C) 9 N down
D) 0 N
E) none of these

Question

Three books (X, Y, and Z) rest on a table. The weight of each book is indicated. The net force acting on book Y is: 
A) 4 N down 
B) 5 N up 
C) 9 N down 
D) 0 N 
E) none of these

Quizplus · Accepted Answer

Since the weight of each book is given and there are no external forces acting on the system, the net force on book Y must be zero according to Newton's 1st Law (law of inertia). Therefore, the correct choice is D) 0 N.

Three Books (X, Y, and Z) Rest on a Table