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mth163
Your 'question form' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
** Question Form_labelMessages **
about my test
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Mr. Smith, Mr. Carter (my doctor) sent a test to you on 3/24 via fax and you sent me a response saying that you may have received only one page of it and that you would search for the rest of the document. Did you receive all of the test? If so what was my grade on it? And if not let me know and I will tell Mr. Carter so he can send it again. Thank you, David
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I did get a second fax, and your test should have been graded in the last batch. Have you checked the gradebook at the Supervised Study ... site?
However I don't recall how you did, which means either that your performance was about as expected (in which case you likely would have done pretty well) or that I haven't really graded the test.
If no grade is posted, email me tomorrow to prompt me to follow up on this.
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Your instructor is trying to gauge the typical time spent by students on these experiments. Please answer the following question as accurately as you can, understanding that your answer will be used only for the stated purpose and has no bearing on your grades:
Approximately how long did it take you to complete this experiment?
Your answer (start in the next line):
2.5hrs
:
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Very good. Your calculations appear to be correct and are well explained, and your results are consistent with results often obained on this experiment.
However the results we usually obtain differ, for reasons I can speculate on but haven't been able to verify, from ideal results. There's nothing at all wrong with your work, but you should be aware of the theoretical predictions.
Theoretically the energy of the rubber band increases more with each additional millimeter than with the last, because more force is being exerted through that distance. So the energy curve would be concave upward--i.e., increasing at an increasing rate.
The frictional force isn't expected to change much as the block slides across the table, nor is it expected to change much with speed. So the energy dissipated against friction as the block slides across the table is pretty much proportional to how far it slides.
We therefore expect that sliding distance vs. pullback will increase at an increasing, not a linear, rate.
I suspect that the reason this doesn't usually occur is that the frictional force does change with speed. In writing this response I've thought of a couple of ways to test that hypothesis. It's not something I'm likely to have time to do anytime soon, but it's definitely high on the list of things I'll do when and if time permits.
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