Discussion 20 solution

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Physics 125 Discussion #20 Solution 1 Problem 1: Stress on the Shin Bone Compressive strength of our bones is important in everyday life. Young’s modulus for bone is about 1.4×10 10 N/m 2 . Bone can take only about a 1.0% change in its length before fracturing. What is the maximum force that can be applied to a bone whose minimum cross-section area is 3.0 cm 2 ? (This is approximately the cross-section area of a tibia, or shin bone, at its narrowest point.) N 10 2 . 4 ) 01 . 0 )( m 10 )(3.0 N/m 10 4 . 1 ( 4 2 4 - 2 10 max 0 max × = × × = ⎛ Δ = L L YA F Problem 2: Hooke’s Law and Young’s Modulus Hooke’s law for a tensile stress can be written as F x =kx , where x is the object’s change in length, and k is the force constant. 1. Write the force constant, k , in terms of the rod’s original length, L 0 , cross-section area, A , and the Young’s modulus, Y. 0 0 0 L
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