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Unformatted text preview: hernandez (ejh742) homework 14 Turner (58120) 1 This printout should have 11 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 (part 1 of 2) 10.0 points A crate is pulled by a force (parallel to the incline) up a rough incline. The crate has an initial speed shown in the figure below. The crate is pulled a distance of 6 . 97 m on the incline by a 150 N force. The acceleration of gravity is 9 . 8 m / s 2 . 1 3 k g = . 3 3 8 1 5 N 1 . 6 9 m / s 24 a) What is the change in kinetic energy of the crate? Correct answer: 410 . 138 J. Explanation: Let : F = 150 N , d = 6 . 97 m , = 24 , m = 13 kg , g = 9 . 8 m / s 2 , = 0 . 338 , and v = 1 . 69 m / s . F N N mg v The workenergy theorem with nonconser vative forces reads W fric + W appl + W gravity = K To find the work done by friction we need the normal force on the block from Newtons law summationdisplay F y = N mg cos = 0 N = mg cos . Thus W fric = mg d cos = (0 . 338) (13 kg) (9 . 8 m / s 2 ) (6 . 97 m) cos24 = 274 . 188 J . The work due to the applied force is W appl = F d = (150 N) (6 . 97 m) = 1045 . 5 J , and the work due to gravity is W grav = mg d sin = (13 kg) (9 . 8 m / s 2 ) (6 . 97 m) sin24 = 361 . 173 J , so that K = W fric + W appl + W grav = ( 274 . 188 J) + (1045 . 5 J) + ( 361 . 173 J) = 410 . 138 J . 002 (part 2 of 2) 10.0 points b) What is the speed of the crate after it is pulled the 6 . 97 m? Correct answer: 8 . 12123 m / s. Explanation: Since 1 2 m ( v 2 f v 2 i ) = K v 2 f v 2 i = 2 K m hernandez (ejh742) homework 14 Turner (58120) 2 v f = radicalbigg 2 K m + v 2 i = radicalBigg 2(410 . 138 J) 13 kg + (1 . 69 m / s) 2 = 8 . 12123 m / s . 003 (part 1 of 3) 10.0 points A block starts at rest and slides down a fric tionless track. It leaves the track horizontally, flies through the air, and subsequently strikes the ground. b b b b b b b b b b b b 418 g 3 . 3m 1 . 8m x v What is the speed of the ball when it leaves the track? The acceleration of gravity is 9 . 81 m / s 2 . Correct answer: 5 . 42494 m / s. Explanation: Let : g = 9 . 81 m / s 2 , m = 418 g , and h 1 = 1 . 5 m ....
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This note was uploaded on 06/14/2011 for the course PHY 303K taught by Professor Turner during the Spring '08 term at University of Texas at Austin.
 Spring '08
 Turner
 Physics, Force, Friction, Work

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