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Bren Forster can kick at 60.7974 m/s but previous calculations of his AP did not take moments of inertia into account (and just assumed the entire leg below the thigh moved at that speed) or did not take the weight of his foot into account when calculating inertia (and assumed the weight of his leg and foot was evenly distributed when in fact it will be heavier at the bottom of his leg because that is where his foot is).
Bren Forster was 84kg at the time of his record breaking kick. A human leg is 4.75% (3.99 kg) and a human foot is 1.43% (1.2012 kg) of the average males body https://robslink.com/SAS/democd79/body_part_weights.htm
It is at the end of his leg or start of his foot (where the leg and foot meet) that is where he strikes with. The moment of inertia of his leg is 1/3 of the mass of his leg since it rotates at the top of his leg at the knee joint and it is the end of his leg that achieved the recorded speed. Assume the entire foot moves at the recorded speed since it is negligible in size compared to the leg so that moment of inertia of his foot is just the mass of his foot.
So the total moment of inertia of his leg and foot is I = (1/3)(3.99 kg) + 1.2012 kg = 2.5312
This means that his RKE is the same as the KE of an object of mass 2.5312 kg that moves in a straight line at the same speed as the end of his leg.
KE = (1/2)(2.5312)(60.7974)^2 = 4678 Joules
(Street level)
Bren Forster was 84kg at the time of his record breaking kick. A human leg is 4.75% (3.99 kg) and a human foot is 1.43% (1.2012 kg) of the average males body https://robslink.com/SAS/democd79/body_part_weights.htm
It is at the end of his leg or start of his foot (where the leg and foot meet) that is where he strikes with. The moment of inertia of his leg is 1/3 of the mass of his leg since it rotates at the top of his leg at the knee joint and it is the end of his leg that achieved the recorded speed. Assume the entire foot moves at the recorded speed since it is negligible in size compared to the leg so that moment of inertia of his foot is just the mass of his foot.
So the total moment of inertia of his leg and foot is I = (1/3)(3.99 kg) + 1.2012 kg = 2.5312
This means that his RKE is the same as the KE of an object of mass 2.5312 kg that moves in a straight line at the same speed as the end of his leg.
KE = (1/2)(2.5312)(60.7974)^2 = 4678 Joules
(Street level)
