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Unformatted text preview: Adams, Russell Homework 4 Due: Oct 5 2006, midnight Inst: Opyrchal, H 1 This print-out should have 8 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. The due time is Central time. 001 (part 1 of 1) 10 points An elevator starts from rest with a constant upward acceleration and moves 1 m in the first 1 . 8 s. A passenger in the elevator is holding a 7 kg bundle at the end of a vertical cord. The acceleration of gravity is 9 . 8 m / s 2 . What is the tension in the cord as the ele- vator accelerates? Correct answer: 72 . 921 N. Explanation: T mg a elevator g Let h be the distance traveled and a the acceleration of the elevator. With the initial velocity being zero, we simplify the following expression and solve for acceleration of the elevator: h = v t + 1 2 a t 2 = 1 2 a t 2 = a = 2 h t 2 . The equation describing the forces acting on the bundle is F net = m a = T- m g T = m ( g + a ) = m g + 2 h t 2 = (7 kg) 9 . 8 m / s 2 + 2 (1 m) (1 . 8 s) 2 = 72 . 921 N . keywords: 002 (part 1 of 1) 10 points A 1259 . 2 kg car is traveling at 30 m / s when the driver takes his foot off the gas pedal. It takes 5 . 1 s for the car to slow down to 20 m / s....
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