As an object falls from rest under gravity, its gravitational potential energy is converted to kinetic energy. When the object hits the ground, its potential energy is zero and its kinetic energy is at a maximum. The work-energy principle states that the change in an object's kinetic energy equals the net work done on it. For impacts, the average impact force multiplied by the distance traveled during impact equals the change in kinetic energy from before to after the impact.

1. As an object falls from rest, its gravitational potential energy is converted to kinetic
energy. Consider a mass m which is falling vertically under the influence of gravity.
Object is falling from rest, therefore initial kinetic energy is zero. Once the object hit
on the ground, height is zero, therefore no potential energy at ground level.
Initial U = Final K
Impact velocity just before the impact is
From work-energy principle, change in the kinetic energy of an object is equal to the
net work done on the object.
For a straight-line collision, the total work done is equal to the average force of
impact times the distance traveled during the impact.
Average impact force x Distance traveled = Change in kinetic energy
Total work done = Kinetic energy just before object hit the ground
U
K
U
K

2. Impact force
Use this simple tool to solve physics problem related to impact force from
falling object.