Question
What information do you need to calculate the kinetic energy and potential energy of a spring? Potential energy due to gravity? How many objects do you need information about for each of these cases?
Final Answer
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Solution video
OpenStax College Physics for AP® Courses, Chapter 7, Problem 24 (Test Prep for AP® Courses)
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Video Transcript
This is College Physics Answers with Shaun Dychko. What information do we need to calculate the kinetic energy and the potential energy of a spring? So we assume that they are talking about the elastic potential energy and ignoring the other types of potential energy for the spring in which case, you need to know just the mass of the spring and its speed in order to calculate its kinetic energy because the formula is one-half mv squared and then for its potential energy, you need to know the spring constant and the amount by which it is compressed and the formula for that is one-half k times Δx squared. So these are the four things you need to know to figure out the kinetic and potential energy of a spring. And then the next question is what do you need to know for finding the potential energy due to gravity? And for that, you need to know the mass of the object because because the potential energy due to gravity is m times gravitational field strength g times the height above some reference level h and so those are the things that you need to know: what is g in the vicinity of this position of this thing and then what is its height and what is its mass? So three things needed in this case for gravitational potential energy and four things for both kinetic and elastic potential energy in the first case.