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Unformatted text preview: Overton, Mays Homework 14 Due: Feb 25 2005, 4:00 am Inst: Turner 1 This printout should have 12 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 1) 10 points Hint: W = ~ S ~ F . Consider a force ~ F with components F x = 27 N, F y = 58 N, and F z = 90 N, as illustrated in the figure below. Work is done when a particle moves up the vertical zaxis a distance of 4 m . ~ F F y F z k & ~S F x The figure is not drawn to scale. What is the angle between the body di agonal which represents the force ~ F and the frontleft edge of the block which represents both the zcomponent F z of the vector ~ F and the vector ~ S the particle traversed? Correct answer: 35 . 4071 . Explanation: Basic Concept: ~ X ~ Y = k ~ X k k ~ Y k cos . (1) Note : ~ S ~ F = ( S k ) ( F x + F y + F z k ) = S F z = (4 m)(90 N) = 360 Nm . Solution: Using Eq. 1, we have = arccos ~ S ~ F k ~ S k k ~ F k ! = arccos S F z  S  q F 2 x + F 2 y + F 2 z = arccos (4 m)(90 N) (4 m)(110 . 422 N) = arccos(0 . 815056) = 35 . 4071 . 002 (part 1 of 1) 10 points An applied force varies with position ac cording to F = k 1 x n k 2 , where n = 3, k 1 = 4 . 4 N / m 3 , and k 2 = 86 N. How much work is done by this force on an object that moves from x i = 6 . 24 m to x f = 18 . 3 m? Correct answer: 120 . 662 kJ. Explanation: Basic Concepts: W = Z ~ F d~s Solution: The work done by a varying force is W = Z x 2 x 1 ~ F d~s. which adds up all the little ~ F ~s parts along the path, taking into account the changing force. Here all the motion is in the direction so ds = dx . W = Z x f x i F dx = Z 18 . 3 m 6 . 24 m (4 . 4 N / m 3 ) x 3 (86 N) / dx = (4 . 4 N / m 3 ) x 4 4 (86 N) x fl fl fl fl 18 . 3 m 6 . 24 m = 4 . 4 N / m 3 4 (18 . 3 m) 4 (6 . 24 m) 4 / (86 N)(18 . 3 m 6 . 24 m) = 120662 J = 120 . 662 kJ ....
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This note was uploaded on 03/22/2008 for the course PHY 303K taught by Professor Turner during the Spring '08 term at University of Texas at Austin.
 Spring '08
 Turner
 Physics, Work

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