Answer:
<em>the maximum height a man can jump from and land rigidly upright on both feet without breaking his legs is 0.34 m</em>
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Explanation:
Mass of a healthy man = 60 kg
energy the bone can take without breaking = 200 J
If a healthy man jumps from a height 'h', he falls with an energy equal to the potential energy due to his initial height above the ground.
initial potential energy of the healthy man = mgh
where m = mass of the man
g = acceleration due to gravity = 9.81 m/s^2
h = the height above ground
==> PE = 60 x 9.81 x h = 588.6h
If we assume that all energy is absorbed in the leg bones in a rigid landing, then we can safely say that this calculated PE for a healthy man is equal to the energy his bone can absorb in the jump without breaking.
equating, we have
200 = 588.6h
<em>the maximum height a man can jump from without breaking his legs = 200/588.6 = 0.34 m</em>
When people jump from a height, the sudden deceleration to zero can impact a big force on the leg bones, shattering them. If the time spent in decelerating to zero is increased, the overall force on the leg bones is reduced greatly.
<em>Bending the knees gradually on landing from a jump from a height, and then rolling increases the time spent decelerating, and reduces the impact force on the legs due to the landing</em>. If you observe carefully you will see that this is what professional stunts men and acrobats do when they jump from a height.
