MasteringPhysics7a

MasteringPhysics7a - MasteringPhysics: Assignment Print View

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MasteringPhysics: Assignment Print View http://session.masteringphysics.com/myct/assignmentPrint?assignmentI. .. 1 of 8 12/19/2007 2:36 AM [ Print View ] PHCC 141: Physics for Scientists and Engineers I - Fall 2007 7a. Potential Energy and Total Mechanical Energy Due at 11:59pm on Thursday, October 4, 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. Work on a Sliding Box A box of mass is sliding along a horizontal surface. Part A The box leaves position with speed . The box is slowed by a constant frictional force until it comes to rest at position . Find , the magnitude of the average frictional force that acts on the box. (Since you don't know the coefficient of friction, don't include it in your answer.) Hint A.1 How to approach the problem Use the work-energy theorem. As applied to this part, the theorem states that the work done by friction is equal to the change in kinetic energy of the box: . Find , , and (which will depend on ), then solve for . Part A.2 Find the initial kinetic energy What is , the kinetic energy of the box at position ? ANSWER: = Part A.3 Find the final kinetic energy What is , the kinetic energy of the box when it reaches position ? ANSWER: = 0 Part A.4 Find the work done by friction Find , the work done by friction on the box. Note that the work done by friction is always negative (i.e., friction always dissipates energy). Express your answer in terms of and other given variables. ANSWER: = Express the frictional force in terms of , , and .
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MasteringPhysics: Assignment Print View http://session.masteringphysics.com/myct/assignmentPrint?assignmentI. .. 2 of 8 12/19/2007 2:36 AM ANSWER: = Part B After the box comes to rest at position , a person starts pushing the box, giving it a speed . When the box reaches position (where ), how much work has the person done on the box? Assume that the box reaches after the person has accelerated it from rest to speed . Hint B.1 How to approach the problem Again, use the work-energy theorem. In this part of the problem, both the person and friction are doing work on the box: . Part B.2
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This note was uploaded on 10/28/2008 for the course PH 141 taught by Professor Toki during the Fall '08 term at Colorado State.

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MasteringPhysics7a - MasteringPhysics: Assignment Print View

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