Dynamics: Kinetic Friction

Question

The coefficient of kinetic friction between an object and the surface upon which it is sliding is 0.46. The weight of the object is 90N. What is the force of friction?

Answer 1

The force of friction for a sliding object is given by the coefficient of kinetic friction times the normal force. The normal force is perpendicular to the surface an object is on, and is equal and opposite to the force of gravity in that direction. So If the object is on a horizontal surface, the normal force is equal to the weight. Since the weight was given, this gives you the information needed.