A stone of mass 0.55 kilograms is released and falls to the ground. Measurements show that the stone has a kinetic energy of 9.8 joules at the point of impact
Ke = (1/2) m v^2 = (1/2) (.55) v^2 = 9.8
v^2 = 35.6
v = 5.97 m/s
to get height
m g h = 0.55 * 9.81 * h = 9.8 Joules
h = 1.82 meters (fell off dad's head)