pdqaltair - i made some mistakes...

J is not only kg.m²/sec² but also N.m and if we calculate now the force of a "fall" with 2100 J which is stopped within 10 cm you get 21000 N of impact force and that is not a small number...

and it is quite in accordance with this graph were the force is shown in relation to a "sturzfaktor" which is basically the height of the fall divided by the length of a rope - in our case this factor would be around 1 but the speed would be less than that of a free fall with 9.81 m/sec² acceleration: