Phy 121
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: ->->->->->->->->->->->-> : I think the minimum tension is 2.4N, the maximum tension is 3N….so the average tension is 2.7N. To do this, I set up a proportion with 10cm=3N and 8cm under 10cm, cross multiplied and divided.
That won't work. That would give you nonzero tensions at lengths less than 8 cm.
• How much work is required to stretch the rubber band from 8 cm to 10 cm?
answer/question/discussion: ->->->->->->->->->->->-> : 2.7N average * 2cm of displacement = 5.4J of work.
• During the stretching process is the tension force in the direction of motion or opposite to the direction of motion?
answer/question/discussion: ->->->->->->->->->->->-> : Opposite.
• Does the tension force therefore do positive or negative work?
answer/question/discussion: ->->->->->->->->->->->-> : Negative
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: ->->->->->->->->->->->-> : ‘dWnet=2.4N*2cm ‘dWnet=4.8J
• 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: ->->->->->->->->->->->-> : KE0=1/2(.02)*0m/s^2 KE0=.01
• At this point how fast will the domino be moving?
answer/question/discussion: ->->->->->->->->->->->-> : a=2.4N/.02kg a=1.2m/s
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30min
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I don't know if I missed something somewhere, but I dont recall learning any formulas or methods for tension in rubber bands. Should I be treating questions like that just like any other force problem?
Most of your work is good, but you have the wrong numbers for the tensions.
Please compare your solutions with the expanded discussion at the link
Solution
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