Phy 231
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.
** **
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:
Answer: minimum tension = 0N, maximum tension = 3N, average tension = 1.5N.
• How much work is required to stretch the rubber band from 8 cm to 10 cm?
answer/question/discussion:
Answer: W=F*ds=1.5N*2cm=3Ncm.
• During the stretching process is the tension force in the direction of motion or opposite to the direction of motion?
answer/question/discussion:
Answer: The tension force is in the opposite direction of motion.
• Does the tension force therefore do positive or negative work?
answer/question/discussion:
Answer: The tension force does negative work.
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:
Answer: F=m*a=.02kg*(-980cm/s/s)=19.6N. W=F*ds=19.6N*8cm=156.8Ncm.
kg * cm/s^2 does not yield Newtons.
Uniform acceleration cannot be assumed here. The force is clearly variable as the length of the rubber band changes.
This should be solved using energy considerations.
Note also that 980 cm/s^2 is not relevant. Gravity is not a consideration here.
• 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:
Answer: vf^2=v0^2+2ads=0+2(980cm/s/s)(8cm)=15680cm^2/s^2, vf=125cm/s. KE=.5mvf^2-0=.5(.02kg)(125cm/s)^2=156J.
• At this point how fast will the domino be moving?
answer/question/discussion:
Answer: 125cm/s.
Units don't work out here either. The answer to thie question depends on the answer to the preceding, and should be obtained using energy conservation.
** **
20 minutes
** **
&#Please see my notes and submit a copy of this document with revisions and/or questions, and mark your insertions with &&&& (please mark each insertion at the beginning and at the end). &#