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Homework Help: Oscillating Spring Graphs

  1. Apr 26, 2015 #1
    How could you graph a potential energy vs. time graph only knowing the position vs. time graph and the velocity vs time graph for a hanging object oscillating up and down on a string?
  2. jcsd
  3. Apr 26, 2015 #2


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    Do you know the elastic potential energy function for a spring?
  4. Apr 26, 2015 #3
  5. Apr 26, 2015 #4


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    So the right move for you would be to do some reading, and come back here with specific questions about that reading. Please post links to your reading when you post your questions. Thanks.
  6. Apr 26, 2015 #5
    i do know some about this topic, but its a practice free response question for the ap physics 1 exam so i thought there would be a short cut. So the object has spring potential energy and gravitational potential energy so its total potential energy is the sum of both?
  7. Apr 26, 2015 #6


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    Staff: Mentor

    Very much like that. The sum of the energies is zero, as the energies in the different modes trades off with motion. What are the different energies involved in this problem? What is the sum over time?
  8. Apr 26, 2015 #7
    The problem asks to sketch the potential energy in the object-spring-Earth system as a function of time. There is kinetic and potential energy. There is two types of potential energy. The only force is the weight. Um, the graph for position vs. time has a maximum of 1m and a minimum of .5m. It looks like a sine graph and it goes up to 2.5 seconds on the x axis. I think to graph the potential vs. time graph you would only need information from the position vs. time graph??? I don't understand how you would find the spring constant because you would need that to find potential energy???
  9. Apr 27, 2015 #8


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    Hi Meg, welcome to PF :smile: !

    If the only force is weight, which I think is pretty constant :rolleyes:, then what causes the oscillation ?

    So much for the help, now comes the lecture :wink::

    Did you, by happenstance, see a template come by when you posted ?
    It looks like this:

    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution​

    and the guidelines (which you should read to maximize your benefits from this forum - and to give you an insight into problem solving seen from various sides) make use of the template compulsory. For good reasons.

    In your case the template has disappeared (a computer problem? :rolleyes:) which is most unfortunate. It would help you sort out what knowledge you do have at hand to tackle the problem. And if you are empty handed, well then you also know what to do.

    Under "Um," in your post #7, you unveil a lot more info than in your problem statement in post #1. You can extract two very important quantities you will need in your relevant equations to establish the sought-after energies. If you want to make good use of assistance from a bunch of top experts, you really should be a bit more complete in your first post. "Help us help you ", so to say.

  10. Apr 27, 2015 #9
    If you want to find the spring constant, have a look at the equations you have and note that there are two forces that act on the object, the spring force and its weight. You've got the maximum and minimum position. So can you find amplitude? If you know amplitude can you find the equilibrium position? Have a go. Once you know the equilibrium position, its pretty easy to find the spring constant.
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