# help me physics

posted by william

The femur is a bone in the leg whose minium cross-sectional area is about 3.60 E-4 m2. A compressional force in excess of 6.90 E4 N will fracture this bone.
(a) Find the maximum stress that this bone can withstand.
1 N/m2

(b) What is the strain that exists under a maximum-stress condition?

1. MathMate

Stress, σ = force/area
=6.9E4/3.6E-4 N/m²
=1.92E8 N/m²

Strain depends on the Young's modulus, E, of bone, which varies from 5 to 30 GPa for a calcium content of 250 mg/g. We will take tha average of 20 GPa.

strain, ε
= σ / E
= 1.92E8 Pa / 20 GPa
= 0.0096 (approx. 1%)

Reference for E:
http://jeb.biologists.org/cgi/reprint/202/18/2495.pdf

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