When you push with a horizontal 15-N force on a book that slides at constant velocity, the force of friction on the book is
A. Slightly more than 15 N
B.0N
C. Slightly less than 15 N
D.15 N

f = 15 N

Explanation:

It is given that, when you push with a horizontal 15-N force on a book that slides at constant  velocity, a frictional force also acts on it. Frictional force is an opposing force. The magnitude of applied force and frictional forces are same. So, the force of friction on the book is equal to 15 N.

1 is a answer of a question