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Phy 121
Your 'cq_1_15.1' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
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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?
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I would guess the minimum tension force would be 0 Newtons and the maximum is 3 Newtons
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Assuming that the tension in the rubber band is 100% conservative (which is not actually the case) what is its elastic potential energy at the 10 cm length?
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Elastic potential energy would be equal to dWnetON, which is 3 J, so Elastic PE = 3 Newtons
(not certain about this)
3 Newtons is a force, not an energy.
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If all this potential energy is transferred to the kinetic energy of an initially stationary 20 gram domino, what will be the velocity of the domino?
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KE = 1/2 * m * v^2; v = sqrt(KE * 2 / m) = sqrt(3 N * 2 / .02 kg) = +- 17.32 m/s
the units of N / kg do not come out m^2 / s^2, so the units of the square root of your quantity will not be m / s. The problem is that the Newton is not a unit of work.
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If instead the rubber band is used to 'shoot' the domino straight upward, then how high will it rise?
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Fnet would then be the original 3 Newtons (Band Force) + Gravity*mass: Fnet = 3 N + (.02 kg * -9.8 m/s^2) = 2.804 N
v = sqrt(2.804N * 2 / .02 kg) = 16.74 m/s, this is vf
a = 2.804N / .02 kg = 140.2 m/s^2
'ds = vf^2 / (2a) = 16.74^2 m/s / (2 * 140.2 m/s^2) = 0.999 meters
My final velocity and acceleration seemed wrong, thus my distance traveled seems wrong.
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For University Physics students:
Why does it make sense to say that the PE change is equal to the integral of the force vs. position function over an appropriate interval, and what is the appropriate interval?
answer/question/discussion: ->->->->->->->->->->->-> :
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15 minutes
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I feel like I am getting a good hold of everything thus far (more practice never hurts) however the whole ideas of non/conservative forces on and by the system can still get me confused.
You didn't get the energy right (see my note). However had you gotten the correct energy the rest of your results would have worked out.
&#See any notes I might have inserted into your document, and before looking at the link below see if you can modify your solutions. If there are no notes, this does not mean that your solution is completely correct.
Then please compare your old and new solutions with the expanded discussion at the link
Solution
Self-critique your solutions, if this is necessary, according to the usual criteria. Insert any revisions, questions, etc. into a copy of this posted document. Mark any insertions with &&&& so they can be easily identified.If your solution is completely consistent with the given solution, you need do nothing further with this problem. &#
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