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Unformatted text preview: homework 08 KIM, JI Due: Oct 24 2007, 4:00 am 1 Question 1, chap 9, sect 1. part 1 of 1 10 points On the way from a planet to a moon astro nauts reach a point where that moons gravi tational pull is as strong as that of the planet. The masses of the planet and the moon are, respectively, 6 . 13 10 24 kg and 7 . 36 10 22 kg. The distance from the center of the planet to the center of the moon is 3 . 7 10 8 m. Determine the distance of this point from the center of the planet. Correct answer: 3 . 33461 10 8 m (tolerance 1 %). Explanation: If r p is the distance from this point to the center of the planet and r m is the distance from this point to the center of the moon, then from the formula GmM p r 2 p = GmM m r 2 m , we obtain q = r m r p = radicalBigg M m M p = radicalBigg 7 . 36 10 22 kg 6 . 13 10 24 kg = 0 . 109574 . On the other hand, r p + r m = R. Eliminating r m from the last two equalities, we obtain r p = R q + 1 = 3 . 7 10 8 m (0 . 109574) + 1 = 3 . 33461 10 8 m . Question 2, chap 9, sect 1. part 1 of 1 10 points A satellite moves in a circular orbit around the Earth at a speed of 6 . 9 km / s. Determine the satellites altitude above the surface of the Earth. Assume the Earth is a homogeneous sphere of radius R earth = 6370 km and mass M earth = 5 . 98 10 24 kg . You will need G = 6 . 67259 10 11 N m 2 / kg 2 Correct answer: 2011 . 03 km (tolerance 1 %). Explanation: The gravitational force provides the cen tripetal acceleration. GmM r 2 = mv 2 r , where M is the mass of the Earth and m is the mass of the satellite. Solving for r yields r = GM v 2 = 8 . 38103 10 6 m Then the height of the satellite above the Earths surface is h = r R earth = 2011 . 03 km Question 3, chap 9, sect 1. part 1 of 2 10 points Given: G = 6 . 67259 10 11 N m 2 / kg 2 . A 3 . 5 kg mass weighs 34 . 3 N on the surface of a planet similar to Earth. The radius of this planet is roughly 7 . 2 10 6 m. Calculate the mass of of this planet. Correct answer: 7 . 61372 10 24 kg (tolerance 1 %). Explanation: By Newtons Law of Universal Gravitation, W = G mM planet r 2 , so M planet = W r 2 Gm = (7 . 2 10 6 m) 2 (6 . 67259 10 11 N m 2 / kg 2 ) 34 . 3 N 3 . 5 kg = 7 . 61372 10 24 kg . homework 08 KIM, JI Due: Oct 24 2007, 4:00 am 2 Question 4, chap 9, sect 1. part 2 of 2 10 points Calculate the average density of this planet. Correct answer: 4869 . 79 kg / m 3 (tolerance 1 %). Explanation: The volume of the planet is V = 4 3 r 3 so its average density is = M planet V = 3 M planet 4 r 3 = 3 (7 . 61372 10 24 kg) 4 (7 . 2 10 6 m) 3 = 4869 . 79 kg / m 3 ....
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This note was uploaded on 05/05/2008 for the course PHY 303K taught by Professor Turner during the Fall '08 term at University of Texas at Austin.
 Fall '08
 Turner
 Physics, Mass, Work

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