HW06-solutions

HW06-solutions - sela (ds39632) HW06 janow (11196) 1 This...

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Unformatted text preview: sela (ds39632) HW06 janow (11196) 1 This print-out should have 14 questions. Multiple-choice 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 5 . 59 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 1 5 N 1 . 7 6 m / s 28 a) What is the change in kinetic energy of the crate? Correct answer: 313 . 63 J. Explanation: Let : F = 150 N , d = 5 . 59 m , = 28 , m = 13 kg , g = 9 . 8 m / s 2 , = 0 . 303 , and v = 1 . 76 m / s . F N N mg v The work-energy 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 . 303) (13 kg) (9 . 8 m / s 2 ) (5 . 59 m) cos28 = 190 . 528 J . The work due to the applied force is W appl = F d = (150 N) (5 . 59 m) = 838 . 5 J , and the work due to gravity is W grav = mg d sin = (13 kg) (9 . 8 m / s 2 ) (5 . 59 m) sin28 = 334 . 342 J , so that K = W fric + W appl + W grav = ( 190 . 528 J) + (838 . 5 J) + ( 334 . 342 J) = 313 . 63 J . 002 (part 2 of 2) 10.0 points b) What is the speed of the crate after it is pulled the 5 . 59 m? Correct answer: 7 . 16578 m / s. Explanation: Since 1 2 m ( v 2 f v 2 i ) = K v 2 f v 2 i = 2 K m sela (ds39632) HW06 janow (11196) 2 v f = radicalbigg 2 K m + v 2 i = radicalBigg 2(313 . 63 J) 13 kg + (1 . 76 m / s) 2 = 7 . 16578 m / s . 003 10.0 points A 1160 kg pile driver is used to drive a steel I-beam into the ground. The pile driver falls 6 . 84 m before contacting the beam, and it drives the beam 9 . 59 cm into the ground be- fore coming to rest. Find the magnitude of the average force the beam exerts on the pile driver while the pile driver is brought to rest. The acceleration of gravity is 9 . 8 m / s 2 ....
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This note was uploaded on 03/09/2012 for the course PHYS 111 taught by Professor Moro during the Spring '08 term at NJIT.

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HW06-solutions - sela (ds39632) HW06 janow (11196) 1 This...

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