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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Seed Question
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?
answer/question/discussion: ->->->->->->->->->->->-> :
The minimum tension would be 0 Newtons, and the maximum would be 3 Newtons.
• 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?
answer/question/discussion: ->->->->->->->->->->->-> :
At the 10 cm length, tension = 3N, and the rubberband had to travel 2 cm to get from 0N to 3N. ‘dW=3N*.02m, or .06J. Since the tension in the band is 100% conservative, there are no nonconservative forces, and ‘DW_NC_BY = 0. We established in Asst. 14 that ‘dw_net_BY= -‘dKE, so we know that - .06J=’dKE. If ‘dW_NC_By + ‘dPE +’dKE = 0, then we can substitute and show that 0+’dPE -.06 J = 0, and ‘dPE = .06J.
the average force is 1.5 N, so the result is half what you give here; otherwise your reasoning is excellent
• 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?
answer/question/discussion: ->->->->->->->->->->->-> :
KE= .5*m*v^2, so, .06 J = .5*.02kg*v^2, and .06 J = .01kg * v^2 and 6 J/kg = v^2, and v=2.45m/s.
• If instead the rubber band is used to 'shoot' the domino straight upward, then how high will it rise?
answer/question/discussion: ->->->->->->->->->->->-> :
The force of the rubberband is still 3 N, and is acting against gravity, which accelerates at 9.8m/s^2. F of gravity = .02kg * 9.8m/s^ 2 = 0.196N, then 3N - .196N = 2.804N. I determined that the work done by the rubber band was .06J, so Fnet*’ds = .06J, or 2.804N * ‘ds = .06J, or ‘ds = .02m.
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25 min
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Very good, but you missed a couple of details. No revision is necessary as long as you understand everything:
&#Please compare your 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. &#