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Unformatted text preview: oldhomewk 16 YOO, HEE 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 ) , where A = 79 N / m and B = 18 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 m . Correct answer: 97 . 872 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 (79 N / m) (2 m) 2 2 (18 N / m 2 ) (2 m) 3 3 bracketrightbigg bracketleftbigg (79 N / m) (3 . 2 m) 2 2 (18 N / m 2 ) (3 . 2 m) 3 3 bracketrightbigg = 97 . 872 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: 97 . 872 J (tolerance 1 %). Explanation: From conservation of energy (conservative force), the change of the kinetic energy is K = U = ( 97 . 872 J) = 97 . 872 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 12 kg slides down a quarter circular track under the influence of gravity with friction present (of coefficient ). The radius of the track is 36 m. The acceleration of gravity is 9 . 8 m / s 2 . 36 m 12 kg Determine the work done by the conserva tive forces. Correct answer: 4233 . 6 J (tolerance 1 %). Explanation: The work done by the conservative force (gravity) is W grav = mg R = (12 kg) (9 . 8 m / s 2 ) (36 m) = 4233 . 6 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 2200 J, what is the work done against friction?...
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This note was uploaded on 05/04/2008 for the course PHY 303K taught by Professor Turner during the Spring '08 term at University of Texas at Austin.
 Spring '08
 Turner
 Force

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