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Unformatted text preview: oldhomewk 16 – PAPAGEORGE, MATT – Due: Feb 24 2008, 4:00 am 1 Question 1, chap 7, sect 2. part 1 of 2 10 points A single conservative force acting on a par ticle varies as vector F = ( Ax + B x 2 ) ˆ ı, where A = 40 N / m and B = 84 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 = 2 . 8 m . Correct answer: 254 . 848 J (tolerance ± 1 %). Explanation: The potential energy is U ( x ) = integraldisplay 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 ) = parenleftbigg Ax 2 1 2 Bx 3 1 3 parenrightbigg parenleftbigg Ax 2 2 Bx 3 3 parenrightbigg = bracketleftbigg (40 N / m) (2 . 8 m) 2 2 (84 N / m 2 ) (2 . 8 m) 3 3 bracketrightbigg bracketleftbigg (40 N / m) (3 . 2 m) 2 2 (84 N / m 2 ) (3 . 2 m) 3 3 bracketrightbigg = 254 . 848 J . Question 2, chap 7, sect 2. part 2 of 2 10 points Find the change in kinetic energy of the particle between the same two points. Correct answer: 254 . 848 J (tolerance ± 1 %). Explanation: From conservation of energy (conservative force), the change of the kinetic energy is K = U = (254 . 848 J) = 254 . 848 J . Question 3, chap 7, sect 1. part 1 of 2 10 points Starting from rest at a height equal to the radius of the circular track, a block of mass 26 kg slides down a quarter circular track under the influence of gravity with friction present (of coefficient μ ). The radius of the track is 30 m. The acceleration of gravity is 9 . 8 m / s 2 . 30 m 26 kg θ Determine the work done by the conserva tive forces. Correct answer: 7644 J (tolerance ± 1 %). Explanation: The work done by the conservative force (gravity) is W grav = mg R = (26 kg) (9 . 8 m / s 2 ) (30 m) = 7644 J . Question 4, chap 7, sect 1. part 2 of 2 10 points If the kinetic energy of the block at the bottom of the track is 5400 J, what is the work done against friction?...
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This note was uploaded on 03/02/2009 for the course PHY 58235 taught by Professor Kleinman during the Spring '09 term at University of Texas at Austin.
 Spring '09
 KLEINMAN
 Physics, Force

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