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Unformatted text preview: Gozick, Brandon Homework 10 Due: Oct 13 2006, 5:00 pm Inst: D Weathers 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 At time t i , the kinetic energy of a particle is 15 . 6 J and its potential energy is 5 . 18 J. At some later time t f , its kinetic energy is 27 . 8 J. If only conservative forces act on the parti cle, what is its potential energy t f ? Correct answer: 7 . 02 J. Explanation: From conservation of energy U i + K i = U f + K f , we obtain U f = K i + U i K f = (15 . 6 J) + (5 . 18 J) (27 . 8 J) = 7 . 02 J . 002 (part 2 of 2) 10 points If the potential energy at time t f is 6 . 22 J, what is the work done by the nonconservative forces acting on the particle? Correct answer: 13 . 24 J. Explanation: The work done by the nonconservative forces is W = K + U = [(27 . 8 J) (15 . 6 J)] + [(6 . 22 J) (5 . 18 J)] = 13 . 24 J . keywords: 003 (part 1 of 2) 10 points A single conservative force acting on a particle varies as ~ F = ( Ax + B x 2 ) , where A = 11 N / m and B = 12 N / m 2 and x is in meters. Find the change in potential energy as the particle moves from x = 3 . 2 m to x 1 = 3 . 7 m . Correct answer: 52 . 565 J. Explanation: The potential energy is U ( x ) = Z x ( Ax + B x 2 ) dx = Ax 2 2 B x 3 3 . If we take U (0) = 0, then the change in the potential energy is U = U ( x 1 ) U ( x ) = Ax 2 1 2 Bx 3 1 3  Ax 2 2 Bx 3 3 = (11 N / m)(3 . 7 m) 2 2 (12 N / m 2 )(3 . 7 m) 3 3  (11 N / m)(3 . 2 m) 2 2 (12 N / m 2 )(3 . 2 m) 3 3 = 52 . 565 J . 004 (part 2 of 2) 10 points Find the change in kinetic energy of the par ticle between the same two points. Correct answer: 52 . 565 J. Explanation: From conservation of energy (conservative force), the change of the kinetic energy is K = U = ( 52 . 565 J) = 52 . 565 J . keywords: 005 (part 1 of 2) 10 points A(n) 2300 g block is pushed by an external force against a spring (with a 25 N / cm spring constant) until the spring is compressed by 13 cm from its uncompressed length. The compressed spring and block rests at the bot tom of an incline of 38 . Gozick, Brandon Homework 10 Due: Oct 13 2006, 5:00 pm Inst: D Weathers 2 The acceleration of gravity is 9...
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 Fall '08
 Weathers
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