We apply a force of 200 Newtons on a wooden Box and push it on the floor at constant velocity. The marginal friction force will be:

Correct answer: (a) 200 Newtons

Explanation

At constant velocity the box has zero acceleration, so by Newton's First Law the net force is zero.

The applied push must be exactly balanced by the kinetic (sliding) friction acting opposite to motion.

Hence friction force = applied force = 200 N.