$81)$ The maximum energy a bone can absorb without breaking is surprisingly small. For a healthy human of mass $60$ kg$,$ experi$-$ mental data show that the leg bones of both legs can absorb about $200$ J$.1.$ From what maximum height could a person jump and land rigidly upright on both feet without breaking his legs? Assume that all the energy is absorbed in the leg bones in a rigid landing. $2.$ People jump from much greater heights than this; explain how this is possible. Hint: Think about how people land when they jump from greater heights.