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PHY 201
Your 'question form' 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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The distance the car travels is an indication of the energy it gained from the proximity of the magnets. Specifically, the frictional force slowing the car typically is about .01 Newton, or 10 milliNewtons. The force exerted on the car by friction is in the direction opposite the car's displacement, so when you calculate the work done by this force, your force and the displacement will have opposite signs (i.e., one will be positive and the other will be negative).
Using the .01 Newton = 10 milliNewton force and your displacement in meters (you likely calculated the displacement in centimeters, so be sure you use the equivalent displacement in meters) find the work done by this force on each of your trials. Give below the initial separation of the magnets, the work done by the frictional force acting on the car in Newtons, the work in milliNewtons, in the form of three numbers per line separated by commas. In the first subsequent line, explain your results and include a detailed sample calculation.
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I understand how to find the initial separation of the magnets and how to use .01N to find the work done by frictional force. Is the question asking for the work done by frictional force in milliNewtons or is it asking for the the work done by kinetic energy in milliNewtons? If it is the first, I understand how to do it, but if it is finding the work done by kinetic energy in milliNewtons, I feel like I'm missing a piece of the information.
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These particular questions don't ask about kinetic energy.
This might have been clarified in class today. In the first approximation the potential energy of the magnet system is converted into kinetic energy, which is then dissipated against friction. So the PE of the magnet system and the max KE are both equal to the work done against friction. In the second approximation, some work is done by friction before maximum KE is attained, so the max KE is a little less than the PE or the work done against friction.