* Constant velocity means zero acceleration. This is a key concept from Newton's laws of motion.

* Newton's First Law: An object at rest stays at rest, and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

* Newton's Second Law: Force equals mass times acceleration (F = ma). Since we want zero acceleration, we need a net force of zero.

Therefore, to maintain constant velocity, you need an applied force equal and opposite to the force of friction. In this case, you would need a 10N force applied in the direction opposite the friction to keep the object moving at a constant velocity.