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?
min tension is 0N, max tension is 3N, average tension is 1.5N
• How much work is required to stretch the rubber band from 8 cm to 10 cm?
3N*.02m = .06J
Work is defined as average force * displacement along the line of the force.
Your displacement is correct. There is no more reason to use the maximum force exerted on the interval than the minimum. 3 N is no better choice than 0 N.
According to your previous answer, 1.5 N is the most reasonable quantity to use for the average tension. If tension is a linear function of length, then this will be precisely correct.
• During the stretching process is the tension force in the direction of motion or opposite to the direction of motion?
The tension force is opposite to the direction of motion.
• Does the tension force therefore do positive or negative work?
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:
If the force is conservative, it will exert the same force at every point as it did when it was being stretched.
What therefore is the average force exerted by the tension?
What is the displacement along the line of the tension, and is this displacement in the direction of the force or opposite? Is the work therefore positive or negative?
How much work is therefore done?
• 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:
In Assignment 11 you saw that `dW_net_ON = `dKE. How does this apply to the given situation?
• At this point how fast will the domino be moving?
answer/question/discussion:
** **
45mins
** **
If I had some examples I could do this no problem. I was trying to use the elastic potential energy to solve this problem but I couldn't apply it.
The idea of elastic potential energy is applicable here, but that's a whole different concept and is unnecessary to this problem.
This problem can be solved using your commonsense conclusion about the average tension, the definition of work, and the most basic work-kinetic energy theorem.
Having reasoned your way through this problem the theory of elastic potential energy becomes accessible. This problem is a step in the direction of understanding what's going on with elastic potential energy.