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Unformatted text preview: gutierrez (ig3472) – HW1 – ditmire – (58216) 1 This printout should have 21 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. 001 10.0 points A certain corner of a room is selected as the origin of a rectangular coordinate system. If a fly is crawling on an adjacent wall at a point having coordinates (2 . 7 m , 8 . 5 m), what is the distance of the fly from the corner of the room? Correct answer: 8 . 91852 m. Explanation: Let : Δ x = 2 . 7 m and Δ y = 8 . 5 m . Using the Pythagorean Theorem, d = radicalBig (Δ x ) 2 + (Δ y ) 2 = radicalBig (2 . 7 m) 2 + (8 . 5 m) 2 = 8 . 91852 m . 002 10.0 points When an object falls through air, there is a drag force ( with dimension M · L / T 2 ) that depends on the product of the surface area of the object and the square of its velocity; i.e. , F air = C A v 2 , where C is a constant. What is the dimension for constant C ? 1. [ C ] = T M 2. [ C ] = M T 3. [ C ] = T · L M 4. [ C ] = M T · L 2 5. [ C ] = T · L 2 M 6. [ C ] = T 2 · L M 7. [ C ] = M T 2 · L 2 8. [ C ] = M L 2 9. [ C ] = M L 3 correct 10. [ C ] = T 2 · L 2 M Explanation: [ F ] = M · L / T 2 , [ A ] = L 2 , and [ v ] = L / T , so [ C ] = [ F ] [ A ] [ v ] 2 = M · L / T 2 L 2 · (L / T) 2 = M · L T 2 · T 2 L 4 = M L 3 . 003 10.0 points Consider a cube of soft, spongy material. Which piece below has the larger density? 1. cutting out a piece of the cube that has oneeighth the volume 2. Unable to determine 3. compressing the cube until it has one eighth the volume correct 4. Densities are the same. Explanation: gutierrez (ig3472) – HW1 – ditmire – (58216) 2 ρ 1 = m V Compressing the cube results in a denser ma terial. Compared to the piece cut out, the compressed piece has density ρ 2 = m 1 8 V = 8 m V = 8 ρ 1 . 004 (part 1 of 3) 10.0 points There are roughly 10 59 neutrons and protons in an average star and about 10 11 stars in a typical galaxy. Galaxies tend to form in clus ters of (on the average) about 10 3 galaxies, and there are about 10 9 clusters in the known part of the Universe. Approximately how many neutrons and protons “#” are there in the known Universe? 1. None of these 2. # ≈ 10 87 3. # ≈ 10 82 correct 4. # ≈ 10 47 5. # ≈ 10 52 6. # ≈ 10 43 Explanation: Let : N n = 10 59 , N s = 10 11 , N g = 10 3 and N c = 10 9 . The number of particles in the observable Universe equals the product of the numbers of particles in each astrophysical unit N nU = N n N s N g N c = ( 10 59 )( 10 11 )( 10 3 )( 10 9 ) = 10 82 neutrons and protons . 005 (part 2 of 3) 10.0 points Suppose all this matter were compressed into a sphere of nuclear matter such that each nuclear particle occupied a volume of 1 . 401 × 10 − 45 m 3 (which is approximately the “volume” of a neutron or proton)....
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This note was uploaded on 04/13/2010 for the course PHY 303K taught by Professor Ditmire during the Spring '10 term at University of Texas at Austin.
 Spring '10
 Ditmire
 Physics

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