(Solution) - Your friend balances a package with mass m 10 -(2025 Original AI-Free Solution)

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Your friend balances a package with mass m = 10 kg on top of his head while standing. The mass of his upper body is M = 55 kg (about 65% of his total mass). Because the spine is vertical rather than horizontal, the force exerted by the sacrum on the spine (
in Fig 8.32) is directed approximately straight up and the force exerted by the back muscles (
) is negligibly small. Find the magnitude of
.