MasteringPhysics7b

MasteringPhysics7b - MasteringPhysics Assignment Print View...

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MasteringPhysics: Assignment Print View http://session.masteringphysics.com/myct/assignmentPrint?assignmentI... 1 of 16 12/19/2007 2:39 AM [ Print View ] PHCC 141: Physics for Scientists and Engineers I - Fall 2007 7b. Potential Energy and Total Mechanical Energy Due at 11:59pm on Monday, October 8, 2007 Hide Grading Details Number of answer attempts per question is: 5 You gain credit for: correctly answering a question in a Part, or correctly answering a question in a Hint. You lose credit for: exhausting all attempts or requesting the answer to a question in a Part or Hint, or incorrectly answering a question in a Part. Late submissions: reduce your score by 100% over each day late. Hints are helpful clues or simpler questions that guide you to the answer. Hints are not available for all questions. There is no penalty for leaving questions in Hints unanswered. Grading of Incorrect Answers For Multiple-Choice or True/False questions, you lose 100% / ( # of options - 1 ) credit per incorrect answer. For any other question, you lose 3% credit per incorrect answer. Potential Energy Calculations Learning Goal: To understand the relationship between the force and the potential energy changes associated with that force and to be able to calculate the changes in potential energy as definite integrals. Imagine that a conservative force field is defined in a certain region of space. Does this sound too abstract? Well, think of a gravitational field (the one that makes apples fall down and keeps the planets orbiting) or an electrostatic field existing around any electrically charged object. If a particle is moving in such a field, its change in potential energy does not depend on the particle's path and is determined only by the particle's initial and final positions. Recall that, in general, the component of the net force acting on a particle equals the negative derivative of the potential energy function along the corresponding axis: . Therefore, the change in potential energy can be found as the integral , where is the change in potential energy for a particle moving from point 1 to point 2, is the net force acting on the particle at a given point of its path, and is a small displacement of the particle along its path from 1 to 2. Evaluating such an integral in a general case can be a tedious and lengthy task. However, two circumstances make it easier: Because the result is path-independent , it is always possible to consider the most straightforward way to reach point 2 from point 1. 1. The most common real-world fields are rather simply defined. 2. In this problem, you will practice calculating the change in potential energy for a particle moving in three common force fields. Note that, in the equations for the forces, is the unit vector in the x direction, is the unit vector in the y direction, and is the unit vector in the radial direction in case of a spherically symmetrical force field.
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