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Unformatted text preview: Zzztayloe, Rex – Homework 11 – Heinz – 81204 – Nov 04, 2004 1 This printout should have 13 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. The due time is Central time. 001 (part 1 of 1) 10 points Bone has a Young’s modulus of about 1 . 8 × 10 10 Pa. Under compression, it can withstand a stress of about 1 . 55 × 10 8 Pa before breaking. Assume that a femur (thigh bone) is 0 . 46 m long, and calculate the amount of compression this bone can withstand before breaking. Correct answer: 3 . 96111 mm. Explanation: Given : Stress = 1 . 55 × 10 8 Pa , L = 0 . 46 m , and Y = 1 . 8 × 10 10 Pa . The amount of compression Δ L is given by Y = µ F A ¶µ L Δ L ¶ = (Stress) µ L Δ L ¶ Δ L = L (Stress) Y = (0 . 46 m) ( 1 . 55 × 10 8 Pa ) 1 . 8 × 10 10 Pa · 1000 mm 1 m = 3 . 96111 mm . 002 (part 1 of 1) 10 points A wooden platform is suspended from a ceil ing by four steel wires at its four corners. Each wire is 7 . 2 m long and of diameter of 2 . 6 mm. The Young modulus of steel is 2 × 10 11 N / m 2 . Two people stand at the center of the plat form, and the total weight of the two people and the platform is 1800 N. How much do the wires stretch? Correct answer: 3 . 05125 mm. Explanation: Given the symmetry of the situation, each wire pull with equal force F which is therefore equal to one quarter of the gross weight of the loaded platform, F = W/ 4 . Each wire has crosssection A = π ( d/ 2) 2 (mind the units!) and therefore is stressed by Stress ≡ F/A = W/ 4 π ( d/ 2) 2 = W πd 2 . Given the Young modulus of the steel, this stress produces strain Δ L L = F/A Y = W πY d 2 which means that the wires stretch by Δ L = WL πY d 2 = 3 . 05125 mm . (mind the units). 003 (part 1 of 1) 10 points Calculate the density of sea water at a depth of 734 m where the hydraulic pressure is about 7 . 49 × 10 6 N / m 2 . (The density of sea water at the surface is 1030 kg / m 3 and the bulk modulus of the water is 2 . 1 × 10 9 N / m 2 .) Correct answer: 1033 . 69 kg / m 3 ....
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This note was uploaded on 07/02/2011 for the course PHYS 201 taught by Professor Woodahl during the Fall '09 term at Indiana.
 Fall '09
 WOODAHL
 Physics, Work

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