1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Elastic Potential Energy

  1. Jun 18, 2017 #1
    Screen%20Shot%202017-06-18%20at%205.57.22%20PM_zpsud1w1rvc.png

    Screen%20Shot%202017-06-18%20at%205.57.12%20PM_zpskyksz9kc.png

    [​IMG] 1. The problem statement, all variables and given/known data
    Which of the following Graphs BEST illustrates the potential energy vs. time for the system in Figure 1, where t=0 is defined as the time at which the incident box 1st contacts the box on the spring?

    My question is why can't the Elastic PE be negative?
    The answer is A

    2. Relevant equations
    Using Conservation of Energy
    1/2mv2 = 1/2kx2

    3. The attempt at a solution
    I Choose C because I knew that at the start, all the energy would be kinetic energy, thus the potential energy must be 0. In addition, I also knew that the graph of a spring must be a sin or cos graph. Once the spring was compressed to the right, it would be positive. However, once the spring travels to the left wouldn't the PE be negative, since the displacement would be negative once it passed the equilibrium point in the spring?

    Thanks.
     
  2. jcsd
  3. Jun 19, 2017 #2

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    Because energy is never negative, unless you are expressing relative energy levels.
    The elastic PE is ½kx2. If x is negative, does that make that expression negative?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Elastic Potential Energy
Loading...