What is work done by a person in moving a block of mass 2kg on a frictionless floor up to a distance of 5m?

If the floor is truly frictionless, then ANY force, no matter how small, applied for

ANY time, no matter how short, will set the block in motion. The force can then

be taken away, because on a frictionless surface, NO force is required in order

to keep the block moving.

The work done is equal to the kinetic energy you want the block to have. That

can be as much or as little as you feel like giving it.