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Unformatted text preview: min (mm64262) – Homework 2 – lee – (GEDB00864) 1 This print-out should have 18 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points A light, inextensible cord passes over a light, frictionless pulley with a radius of 5 . 2 cm. It has a(n) 17 kg mass on the left and a(n) 6 . 8 kg mass on the right, both hanging freely. Initially their center of masses are a vertical distance 2 . 9 m apart. The acceleration of gravity is 9 . 8 m / s 2 . 2 . 9 m 5 . 2 cm ω 17 kg 6 . 8 kg At what rate are the two masses accelerat- ing when they pass each other? Correct answer: 4 . 2 m / s 2 . Explanation: Let : R = 5 . 2 cm , m 1 = 6 . 8 kg , m 2 = 17 kg , h = 2 . 9 m , and v = ω R . Consider the free body diagrams 17 kg 6 . 8 kg T T m 2 g m 1 g a a Since the larger mass will move down and the smaller mass up, we can take motion downward as positive for m 2 and motion up- ward as positive for m 1 . Apply Newton’s second law to m 1 and m 2 respectively and then combine the results: For mass 1: summationdisplay F 1 : T- m 1 g = m 1 a (1) For mass 2: summationdisplay F 2 : m 2 g- T = m 2 a (2) We can add Eqs. (1) and (2) above and obtain: m 2 g- m 1 g = m 1 a + m 2 a a = m 2- m 1 m 1 + m 2 g = 17 kg- 6 . 8 kg 17 kg + 6 . 8 kg (9 . 8 m / s 2 ) = 4 . 2 m / s 2 . T = m 1 ( g + a ) = (6 . 8 kg) (9 . 8 m / s 2 + 4 . 2 m / s 2 ) = 95 . 2 N . 002 (part 1 of 3) 10.0 points A boy throws a ball upward. Compare the magnitudes of the gravitational accelerations at three points along the path of the ball. Point A is before the ball reaches the top. a) Point A on the way up. b) Point B is at the top. c) Point C is after it has passed the top and on the way down. min (mm64262) – Homework 2 – lee – (GEDB00864) 2 B A C The magnitudes of the acceleration are re- lated as 1. a A < a B . 2. a A = g . correct Explanation: The gravitational acceleration near the sur- face of the earth is a constant, so the correct choice is a A = g . 003 (part 2 of 3) 10.0 points The magnitudes of the acceleration are re- lated as 1. a B = 0 . 2. a B > a C . 3. a B = a A . correct Explanation: The gravitational acceleration near the sur- face of the earth is a constant, so the correct choice is a B = a A . 004 (part 3 of 3) 10.0 points The magnitudes of the acceleration are re- lated as 1. a C < a B and a A < a B . 2. a C = a B = a A . correct Explanation: The gravitational acceleration near the sur- face of the earth is a constant, so the correct choice is a C = a B = a A . 005 (part 1 of 2) 10.0 points A block with a mass of 6.3 kg is held in equilibrium on a frictionless incline of 31.0 ◦ by the horizontal force vector F , as shown....
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