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Unformatted text preview: Muraj, Hamza Homework 15 Due: Feb 27 2006, 4:00 am Inst: Florin 1 This printout should have 11 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. The due time is Central time. 001 (part 1 of 2) 10 points A person lifts a 4.3 kg cement block a vertical distance of 1.1 m and then carries the block horizontally a distance of 8.1 m. The acceleration of gravity is 9 . 81 m / s 2 . a) Determine the work done by the person in the process. Correct answer: 46 . 4013 J. Explanation: Basic Concept: W = F d cos Given: m = 4 . 3 kg d 1 = 1 . 1 m d 2 = 8 . 1 m g = 9 . 81 m / s 2 1 = 0 2 = 90 Solution: W person = F g d 1 cos 1 + F g d 2 cos 2 = mg d 1 cos0 + mg d 2 cos90 = mg d 1 = (4 . 3 kg) ( 9 . 81 m / s 2 ) (1 . 1 m) = 46 . 4013 J . 002 (part 2 of 2) 10 points b) Determine the work done by the force of gravity in the process. Correct answer: 46 . 4013 J. Explanation: Given: 1 = 180 Solution: W gravity = F g d 1 cos 1 + F g d 2 cos 2 = mg d 1 cos180 + mg d 2 cos90 = mg d 1 = (4 . 3 kg)(9 . 81 m / s 2 )(1 . 1 m) = 46 . 4013 J . 003 (part 1 of 1) 10 points A car and driver weighing 7120 N passes a sign stating Bridge Out 25 . 3 m Ahead. She slams on the brakes, and the car decelerates at a constant rate of 12 . 3 m / s 2 . The acceleration of gravity is 9 . 8 m / s 2 . What is the magnitude of the work done stopping the car if the car just stops in time to avoid diving into the water? Correct answer: 226089 J. Explanation: The mass of the car is m = W g = 7120 N 9 . 8 m / s 2 = 726 . 531 kg . The force exerted by the brake is F = ma = (726 . 531 kg)(12 . 3 m / s 2 ) = 8936 . 33 N . Therefore, the work done by the brake on the car is W = F x = (8936 . 33 N)(25 . 3 m) = 226089 J ....
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 Spring '09
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