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.
Geologists do not use a minerals color or streak to identify them because some minerals can have the same streak and color but the correct answer is b) color
