Question 5
A box is pulled along a floor with a horizontal force of 14 N and slides at a constant velocity. What is the dynamic friction between the box and the floor?
The right answer is the one marked above.
14 N. Constant velocity means no acceleration, so by F = m a the unbalanced force is zero and the forces balance.
friction = applied force = 14 N
"0 N" confuses no unbalanced force with no friction. If friction were really zero the box would accelerate under the 14 N pull.