Question

The force of friction acting on a box sliding across the floor is 100 N. In Newtons, what amount of force needs to be applied in the opposite direction in order to maintain a constant velocity?

Answer 1

100 N or less.

A constant velocity means that there a net force. A force is mass times acceleration, and acceleration is the change in velocity. When velocity is constant, acceleration is 0.

That's why the force needs to be equal to the force of friction for it to maintain a constant velocity. However, if the applied force is less than 100 N, the force of friction will scale to resist any motion.