ch07-potential-energy-and-energy-conservation

# ch07-potential-energy-and-energy-conservation -...

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11/3/08 6:01 PM MasteringPhysics Page 1 of 17 http://session.masteringphysics.com/myct?productID=22377 [ Print View ] Introductory mechanics Chapter 07 - Potential Energy And Energy Conservation Due at 11:59pm on Tuesday, October 21, 2008 View Grading Details 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 Part not displayed Express the frictional force in terms of , , and . 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? [ Print ]

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11/3/08 6:01 PM MasteringPhysics Page 2 of 17 http://session.masteringphysics.com/myct?productID=22377 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 Find the work done by friction What is , the total work done by friction on the box as the person pushes it from position to position ? Hint B.2.a Finding the force of friction The normal force on the box is unchanged from partA. Therefore, the force of friction is the same in this part as in part A. Answer in terms of given variables. (Your answer should not include .) ANSWER: = Part B.3 Find the change in kinetic energy What is , the change in kinetic energy of the box from the moment it is at position to the moment it is at position ? ANSWER: = Express the work in terms of , , , , and . ANSWER: = Introduction to Potential Energy Learning Goal: Understand that conservative forces can be removed from the work integral by incorporating them into a new form of energy called potential energy that must be added to the kinetic energy to get the total mechanical energy. The first part of this problem contains short-answer questions that review the work-energy theorem. In the second part we introduce the concept of potential energy. But for now, please answer in terms of the work-energy theorem. Work-Energy Theorem
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## This note was uploaded on 11/29/2009 for the course PHYSICS idk taught by Professor Idk during the Winter '09 term at Art Institute.

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ch07-potential-energy-and-energy-conservation -...

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