An object is moving at a constant velocity of 20 m/s across a frictionless floor. The force needed to keep the object moving at the same speed is:

Newton's first law of motion states that an object at rest stays at rest, and an object in motion stays in motion at a constant velocity unless acted on by a net external force.

This means that an object at rest will tend to stay at rest, while an object in motion will tend to stay in motion.

This is also referred to as the law of inertia.

The floor has no friction.

Because there is no external force acting on the object, Newton's first law of motion states that it will remain in its original state of motion.

As a result, no force is required to keep the object moving at a constant velocity.