Question

When someone falls, the kinetic energy the person has upon reaching the floor is the amount of what energy lost by falling through height?

Answer 1

potential energy

with a minus sign because the displacement while stopping and the force from floor are in opposite directions  cos  = cos 180 =  1  . The floor removes energy from the system, so it does negative work. The kinetic energy the person has upon reaching the floor is the amount of potential energy lost by falling through height.