I believe that this calculator generates answers assuming that the only force acting on a falling object after it has encountered a stopping surface is the force of the stopping surface. The calculator needs to factor in gravity throughout the whole fall. Would someone else please verify? http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html Click Mechanics, work-energy principle, and then impact force of falling object, and "Since you know velocity, mass, and kinetic energy, can you predict the force of impact?" Example numbers: m=50kg, h=10m, d=5m stopping force should be about 1480N, but the calculator is saying 980N.