oldhw1_s - oldhomewk 01 YOO, HEE Due: Jan 17 2008, 4:00 am...

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Unformatted text preview: oldhomewk 01 YOO, HEE Due: Jan 17 2008, 4:00 am 1 Question 1, chap 1, sect 5. part 1 of 1 10 points A newly discovered giant planet has an av- erage radius 17 times that of the Earth and a mass 181 times that of the Earth. Calculate the ratio of the new planets den- sity to the Earths density. Correct answer: 0 . 036841 (tolerance 1 %). Explanation: Let : R n = 17 R E and m n = 181 m E . Density is the ratio of mass to volume, = m V . A spherical planet of average radius R has volume 4 3 R 3 and hence density = m 4 3 R 3 . For two planets of respective radii R 1 and R 2 and masses m 1 and m 2 we have 1 2 = m 1 4 3 R 3 1 m 2 4 3 R 3 2 = parenleftbigg m 1 m 2 parenrightbigg parenleftbigg R 1 R 2 parenrightbigg 3 = 181 (17) 3 = . 036841 . Question 2, chap 1, sect 5. part 1 of 1 10 points A sphere of metal has a radius of 5 . 7 cm and a density of 6 . 81 g / cm 3 . What is the mass of the sphere? Correct answer: 5282 . 75 g (tolerance 1 %). Explanation: Let : r = 5 . 7 cm and = 6 . 81 g / cm 3 . Density is mass per unit volume, so = m V m = V = 4 3 r 3 = ( 6 . 81 g / cm 3 ) 4 3 (5 . 7 cm) 3 = 5282 . 75 g . Question 3, chap 1, sect 99. part 1 of 1 10 points A cylinder, 20 cm long and 8 cm in radius, is made of two different metals bonded end- to-end to make a single bar. The densities are 5 g / cm 3 and 6 . 1 g / cm 3 . 2 c m 8 cm What length of the lighter metal is needed if the total mass is 21565 g? Correct answer: 13 . 4041 cm (tolerance 1 %). Explanation: Let : = 20 cm , r = 8 cm , 1 = 5 g / cm 3 , 2 = 6 . 1 g / cm 3 , and m = 21565 g . oldhomewk 01 YOO, HEE Due: Jan 17 2008, 4:00 am 2 Volume of a bar of radius r and length is V = r 2 and its density is = m V = m r 2 so that m = r 2 x x r Let x be the length of the lighter metal; then x is the length of the heavier metal....
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This note was uploaded on 05/04/2008 for the course PHY 303K taught by Professor Turner during the Spring '08 term at University of Texas at Austin.

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oldhw1_s - oldhomewk 01 YOO, HEE Due: Jan 17 2008, 4:00 am...

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