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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
This page maintained by Michael Richmond. Last modified Dec 4, 1997.
Copyright © Michael Richmond.
This work is licensed under a Creative Commons License.