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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