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Tarzan, Lord of the Jungle, has a femur (thigh-bone) which is 4 cm in diameter and 45 cm long, under normal conditions. One day, to show off to Jane, he lifts Tantor the elephant (mass = 3000 kg) over his head.

Question 1: What is the stress on Tarzan's femur?

Force (mass of Tantor)*(g) Answer: stress = ------------------- = ---------------------- cross-section area pi*radius*radius (3000 kg)*(9.8 m/s^2) 2.94x10^3 N = ------------------------ = ---------------- 3.14*(0.02 m)*(0.02 m) 1.26x10^(-3) m^2 = 2.34x10^7 N/m^2

Under the stress of Tantor's weight, Tarzan's femur compresses to a length of 44.5 cm.

Question 2: What is the strain exhibited by Tarzan's femur?

change in length 45 cm - 44.5 cm 0.5 cm Answer: strain = ----------------- = ---------------- = ---------- original length 45 cm 45 cm = 0.011 (no units)

Question 3: Calculate Young's modulus for Tarzan's femur.

Answer: the formula involving Young's modulus is stress = Young's modulus * strain Therefore, stress 2.34x10^7 N/m^2 Young's modulus = ------------ = ----------------- strain 0.011 = 2.1x10^9 N/m^2

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This page maintained by Michael Richmond.
Last modified Dec 4, 1997.
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