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PHY 201
Your 'cq_1_14.1' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
** CQ_1_14.1_labelMessages **
A rubber band begins exerting a tension force when its length is 8 cm. As it is stretched to a length of 10 cm its tension increases with length, more or less steadily, until at the 10 cm length the tension is 3 Newtons.
• Between the 8 cm and 10 cm length, what are the minimum and maximum tensions, and what do you think is the average tension?
answer/question/discussion: ->->->->->->->->->->->-> :
1 N @ 8 cm and 3 N @ 10 cm. The average tension would be about 2 N
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Good thinking but the tension is zero up to the point where the rubber band begins exerting a force. At that point the tension doesn't suddenly jump to 1 Newton; it is still pretty much 0 and starts increasing from there.
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• How much work is required to stretch the rubber band from 8 cm to 10 cm?
answer/question/discussion: ->->->->->->->->->->->-> :
I have no clue, where can I find this material discussing tension and force? I keep skimming through the notes and must be overlooking it.
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You would have encountered the definition of work in Introductory Problem Set 3, and elsewhere. Work is the product of aveage force and displacement.
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• During the stretching process is the tension force in the direction of motion or opposite to the direction of motion?
answer/question/discussion: ->->->->->->->->->->->-> :
Tension force would be opposite of the direction of motion
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• Does the tension force therefore do positive or negative work?
answer/question/discussion: ->->->->->->->->->->->-> :
If it is opposite direction of motion, would it not be doing negative work?
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That's right. When average force and displacement are in opposite directions, then whichever direction we choose as positive, one of the quantities is positive and the other negative. Thus their product is negative.
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The rubber band is released and as it contracts back to its 8 cm length it exerts its tension force on a domino of mass .02 kg, which is initially at rest.
• Again assuming that the tension force is conservative, how much work does the tension force do on the domino?
answer/question/discussion: ->->->->->->->->->->->-> :
I am so confused with this material. What is the acceleration that is acting on it?
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The acceleration is variable, in which case it's usually best to go with the concept of work and energy.
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• Assuming this is the only force acting on the domino, what will then be its kinetic energy when the rubber band reaches its 8 cm length?
answer/question/discussion: ->->->->->->->->->->->-> :
Again, sooooo confused
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• At this point how fast will the domino be moving?
answer/question/discussion: ->->->->->->->->->->->-> :
No clue because i am lost with the material above.
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5 mins because I don't have a clue.
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I think you've got a pretty good clue, and I don't think it will be too difficult for you to resolve this.
See also Class Notes starting with #9, I believe. Work and energy are addressed at some point in most of these documents.
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The bottom line here is that work is the product of average force and displacement.
It's also necessary that you understand the relationship between work and kinetic energy.
Once more, check out the introductory problem sets (set 3) and Class Notes.
If you have questions in the meantime, use the Question Form and I'll be glad to answer.
&#Please see my notes and submit a copy of this document with revisions, comments and/or questions, and mark your insertions with &&&& (please mark each insertion at the beginning and at the end).
Be sure to include the entire document, including my notes. &#
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