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Homework Help: Conservation of Energey & Kinematics

  1. Apr 5, 2010 #1
    1. The problem statement, all variables and given/known data

    We are working on Conservation of Energy, which for the most part I understand.
    In this lab we have a spring that we have to figure out how far we have to stretch it when it's on an apparatus in order for it to land 3.75 m away on a target on the ground. Me and my partner did this and got the target. But we did it differently then the lab told us to ( the teacher didn't care). We used the range function to find the initial velocity we needed. The lab wanted us to use kinematics. Instead of trying to write everything out I scanned

    what I have so far with all the work shown:
    http://i95.photobucket.com/albums/l149/adnamaplz/Scan100950000.jpg" [Broken]

    And the lab itself w/ a drawing:
    http://i95.photobucket.com/albums/l149/adnamaplz/Scan100950001.jpg" [Broken]

    2. Relevant equations

    see work

    3. The attempt at a solution

    So the question is: What happened? Why does the lab work as it does? (talk about conservation of energy and kinematics)

    Since I didn't use kinematics my answer is kinda a guess:

    What Happened: Using Conservation of Energy we set up the equation Potential Energy = Kinetic energy + Gravitational Potential Energy. Then we used the Range function to find out what the needed initial velocity was. We found the elastics constant by making the line of best fit and finding the slope. After solving for delta x of the spring we shot the spring and it landed on the desired target.
    Why: I'm not sure how to explain how it worked, this is the part i'm lost on
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Apr 5, 2010 #2


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    Homework Helper

    I don't understand, you did use kinematics and conservation of energy. The range equation you used was derived from the parabolic kinematic equations.

    It most likely worked well enough due to the air resistance being small.
  4. Apr 5, 2010 #3
    When I say kinematics I mean just eh equations my teacher gave us. We never used the range function in class. We were supposed to figure it out with eh regular equations.
  5. Apr 6, 2010 #4


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    I'm pretty sure had you started with the general equations you'd have ended up using the equation you used.
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