Phy 231
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.
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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, and what do you think is the average tension?
answer/question/discussion: ->->->->->->->->->->->-> :
The tension at 8cm is 0N and at 10cm it is 3N. The average tension is 0N+3N / 2 = 1.5N.
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• How much work is required to stretch the rubber band from 8 cm to 10 cm?
answer/question/discussion: ->->->->->->->->->->->-> :
Force = 3N, ds = 2cm
Work = 3N * .02m = .06 J
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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: ->->->->->->->->->->->-> :
The tension is in the direction of motion of the band, or in the direction of the stretch.
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• Does the tension force therefore do positive or negative work?
answer/question/discussion: ->->->->->->->->->->->-> :
This means that the tension does positive work.
While the system is being stretched, the tension force acting on the domino is in the direction opposite that of its motion, so it does negative work.
More about the tension force:
Tension forces act throughout the rubber band. If we regard the mass (and therefore the weight) of the rubber band as negligible, tension exerts equal and opposite forces at every point of the band, except its ends.
At each end, since the rubber band exists only on one side of that end, there is no equal and opposite tension force so the tension acts in only one direction, toward the opposite end.
Thus the tension force at the end attached to the domino acts in the direction from the attached end to the opposite end of the rubber band.
During the stretching process, this is opposite the direction of motion.
After release, the direction of motion will be toward the opposite end of the band, so the tension force and displacement will be in the same direction.
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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: ->->->->->->->->->->->-> :
The tension force will do .06J of work on the domino. ????????Actually would it be -.06J because the positive direction was stretching the band, so acting on the domino, it would go in the opposite direction??????????
See my note above.
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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: ->->->->->->->->->->->-> :
Kinetic energy + net work = 0
So, KE -.06J = 0
The KE = .06J
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• At this point how fast will the domino be moving?
answer/question/discussion: ->->->->->->->->->->->-> :
.06 J = .02 kg (v^2)
V^2 = 3 m^2/s^2
V = 1.73 m/s
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20 minutes
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&#Very good work. Let me know if you have questions. &#