A horizontal force of 120 N is required to push a bookcase across the floor at a constant velocity how much is the friction force that acts on the sliding bookcase

The Friction Force that acts on a sliding bookcase is - 120 N

Explanation:

Frictional force is the force developed by the two surfaces where they contact and slide against each other. They mainly affected by amount of force impelled them together and by the angle and position of the object. Frictional Force F = Coefficient of friction * normal force At a constant velocity, there will be no acceleration and the net force will be zero.

Net Force = m * a = 0

120 - Friction = 0

Friction Force = - 120 N