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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.
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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: ->->->->->->->->->->->-> :
Minimum tension= just over 0 newtons
Maximum tension= 3 newtons
Average tension= 3/2= 1.5 newtons
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How much work is required to stretch the rubber band from 8 cm to 10 cm?
answer/question/discussion: ->->->->->->->->->->->-> :
Work= average force*displacement
work= 1.5newtons*2cm
work= 3 newton*cm
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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: ->->->->->->->->->->->-> :
During stretching, the tension force is opposite the direction of motion, because it is resisting motion.
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Does the tension force therefore do positive or negative work?
answer/question/discussion: ->->->->->->->->->->->-> :
Since it acts against motion it is doing negative work.
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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 does 3 newtons of work on the dominoe in the direction of the tension force.
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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: ->->->->->->->->->->->-> :
acceleration= 3 newton/.02kg
acceleration= 150 newton/kg= 150m/s^2
Vf2=2*150m/s^2*.02m
Vf=2.5m/s
KE=.5*.02kg*(2.5m/s)^2
KE=.5*.02kg*2.5m2/s2
KE= 0.025kg*m2/s2
@& Good, but 3 N is the maximum force, not the average force. If you use the 1.5 N average force to get the average acceleration, you'll get a lower answer ( around 1.7 m/s).
Note that you could also set 1/2 m v^2 equal to 3 N * cm and solve for v. This would lead to the same result.*@
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At this point how fast will the domino be moving?
answer/question/discussion: ->->->->->->->->->->->-> :
2.5m/s
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@& No revision is necessary but be sure to check my notes. Your approach was excellent and you made only one common error.
You will understand my note, but if you do have questions of course they are welcome.*@