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Unformatted text preview: oldhomewk 37 PAPAGEORGE, MATT Due: Apr 28 2008, 4:00 am 1 Question 1, chap 18, sect 3. part 1 of 1 10 points In testing a new material for shielding spacecraft, 149 small ball bearings, each mov ing at a supersonic speed of 415.7 m/s, collide headon and elastically with the material dur ing a 0.590 min interval. If the bearings each have a mass of 8.6 g and the area of the tested material is 0.74 m 2 , what pressure is exerted on the material? Correct answer: 40 . 6687 Pa (tolerance 1 %). Explanation: Basic Concepts: P = F A Conservation of momentum: p = F t Elastic collision: v f = v i Given: t = 0 . 590 min N = 149 m = 8 . 6 g v = 415 . 7 m / s A = 0 . 74 m 2 Solution: p = mv f mv i = m ( v i ) mv i = 2 mv i and F = p t For one bearing, P = vextendsingle vextendsingle vextendsingle p t vextendsingle vextendsingle vextendsingle A = 2 mv A t For all of the bearings, P = N parenleftbigg 2 mv A t parenrightbigg = 2(149)(8 . 6 g)(415 . 7 m / s) (0 . 74 m 2 )(0 . 59 min) parenleftbigg 1 min 60 s parenrightbigg parenleftbigg 1 kg 1000 g parenrightbigg = 40 . 6687 Pa Question 2, chap 18, sect 4. part 1 of 2 10 points A simple Utube that is open at both ends is partially filled with a liquid of density 614 kg / m 3 . Water is then poured into one arm of the tube, forming a column 15 cm in height, as shown in the following diagram. The density of heavy liquid is 1000 kg / m 3 . h 1 15 cm light liquid 614 kg / m 3 heavy liquid 1000 kg / m 3 What is the difference, h 1 , in the heights of the two liquid surfaces? Correct answer: 9 . 42997 cm (tolerance 1 %). Explanation: Basic Concepts: gauge pressure, varia tion of pressure with depth Because the liquid in the Utube is static, the pressure exerted by the heavy liquid column of height in the right branch of the tube must balance the pressure exerted by the liquid of height h 1 + in the left branch. Therefore, P + ( + h 1 ) g = P + h g . oldhomewk 37 PAPAGEORGE, MATT Due: Apr 28 2008, 4:00 am...
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 Spring '09
 KLEINMAN
 Physics

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