if you fall,
a force will hit you equal to 0 - (ur initial momentum) all over the length of time it takes for your momentum to be zero..
work is change in kinetic energy,, so the earth does work on you (negative work)
the distance required to decelerate you to a stop is almost zero coz it's instantaneous.
so the force that will hit you is work/distance... since the distance is very small, the force is large, that explains why it hurts (if you fall at high velocitie)..