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Unformatted text preview: Pickering, Tracey Homework 13 Due: Feb 22 2006, noon Inst: Drummond 1 This print-out should have 12 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 2) 10 points Assume your mass is 60 kg. The acceleration due to gravity is 9 . 8 m / s 2 . How much work against gravity do you do when you climb a flight of stairs 3 . 6 m high? Correct answer: 2116 . 8 J. Explanation: Let : m = 60 kg , g = 9 . 8 m / s 2 , and h = 3 . 6 m . W = mg h = (60 kg)(9 . 8 m / s 2 )(3 . 6 m) = 2116 . 8 J . 002 (part 2 of 2) 10 points Consider the energy consumed by a 150 W light bulb in an hour. How many flights of stairs would you have to climb to equal the work of the lightbulb? Correct answer: 255 . 102 . Explanation: For the light bulb: E = P t = (150 W)(3600 s) = 540000 J , n = E W = 540000 J 2116 . 8 J = 255 . 102 . 003 (part 1 of 1) 10 points A block of mass m is pushed a distance D up an inclined plane by a horizontal force F . The plane is inclined at an angle with respect to the horizontal. The block starts from rest and the coefficient of kinetic friction is k . m D k F What is the final speed of the block? 1. v = r 2 m ( F cos - mg sin + k N ) D 2. v = r 2 m ( F sin + k N ) D 3. v = r 2 m ( F cos - mg sin - k N ) D correct 4. v = r 2 m ( F cos + mg sin ) D 5. v = r 2 m ( F cos - mg sin ) D 6. v = r 2 m ( F sin - k N ) D 7. v = r 2 m ( F cos - k N ) D 8. v = r 2 m ( F cos + mg sin - k N ) D Explanation: The work done by gravity is W grav = mg D cos(90 + ) =- mg D sin ....
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- Fall '08