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Unformatted text preview: lim (kl9356) Homework 17 Weathers (17104) 1 This printout should have 10 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 (part 1 of 2) 10.0 points a) Find the time it takes an object to hit the ground when it is dropped from a height of 67 using the model h = 16 t 2 + s, where s is the initial height, and t is in sec onds. Correct answer: 2 . 04634 sec. Explanation: h = 16 t 2 + 67 The ball hits the ground at h = 0, so 0 = 16 t 2 + 67 16 t 2 = + 67 16 t 2 16 = 67 16 t 2 = 4 . 1875 t 2 = 4 . 1875 t 2 . 04634 Time must be positive, so t 2 . 04634 sec . 002 (part 2 of 2) 10.0 points b) Find the time it takes an object to hit the ground when it is dropped from a height of 134 ft. Correct answer: 2 . 89396. Explanation: h = 16 t 2 + 134 The ball hits the ground at h = 0. Thus the time of fall can be found from 0 = 16 t 2 + 134 16 t 2 = + 134 16 t 2 16 = 134 16 t 2 = 8 . 375 t 2 = 8 . 375 t 2 . 89396 t cannot be negative, so t 2 . 89396 . Note that doubling the distance does not dou ble the time. 003 (part 1 of 2) 10.0 points Given: G = 6 . 67259 10 11 N m 2 / kg 2 Two hypothetical planets of masses 4 10 23 kg and 7 . 7 10 23 kg and radii 4 . 8 10 6 m and 6 . 1 10 6 m, respectively, are at rest when they are an infinite distance apart. Because of their gravitational attraction, they head toward each other on a collision course. When their centertocenter separation is 5 . 5 10 8 m, find their relative velocity. Correct answer: 532 . 822 m / s. Explanation: At infinite separation the potential energy U is zero, and at rest the kinetic energy K is zero. Since energy is conserved we have 0 = 1 2 m 1 v 2 1 + 1 2 m 2 v 2 2 Gm 1 m 2 d . The initial momentum is zero and momentum is conserved, so 0 = m 1 v 1 m 2 v 2 . Combine these two equations to find v 1 = m 2 radicalBigg 2 G d ( m 1 + m 2 ) = 7 . 7 10 23 kg radicalBigg 2 (6 . 67259 10 11 N m 2 / kg 2 ) (5 . 5 10 8 m) (1 . 17 10 24 kg) = 350 . 661 m / s v 2 = m 1 radicalBigg...
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 Fall '08
 Weathers
 Magnetism, Work

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