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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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cq_1_151
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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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Copy the problem below into a text editor or word processor.
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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?
answer/question/discussion: ->->->->->->->->->->->-> : ->->->->->->->->->->->-> :
The minimum tension is 0 Newtons and the maximum tension 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?
answer/question/discussion: ->->->->->->->->->->->-> : ->->->->->->->->->->->-> :
The elastic potential at 10cm is .03 Joules because the work done by the rubber band is .03J because 1.5N*.02m = .03J.
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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?
answer/question/discussion: ->->->->->->->->->->->-> : ->->->->->->->->->->->-> :
The final velocity is the domino will be 1.73m/s because KEf = 1/2mv^2, so .03J = ½*.02kg*v^2, which is 1.73m/s.
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• If instead the rubber band is used to 'shoot' the domino straight upward, then how high will it rise?
answer/question/discussion: ->->->->->->->->->->->-> : ->->->->->->->->->->->-> :
The domino will not leave the ground because it does not have a high enough velocity to leave the ground when met with gravity.
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Any nonzero vertical velocity will carry an object at least a little higher. It will rise until its KE has all been converted to gravitational PE.
No matter what the velocity and what the opposing acceleration, it takes a finite time to bring a mass to rest, and during that interval it does have some displacement.
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&&&&&The domino will rise until its .03J of Kinetic energy have changed into Potential energy.
Given that PE = mg’dy, we can now find the height to be as follows:
.03J = .02kg*9.8m/s^2*’dy
.03J = .196kgm/s^2*’dy
.153m = ‘dy
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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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&#Your work looks very good. Let me know if you have any questions. &#