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!

Best solution? for work done on a spring.

  1. Jun 11, 2013 #1
    1. The problem statement, all variables and given/known data
    GIVEN: Force constant (k) = 170N/m. Displaced 10cm (0.1m) from equilibrium position.
    REQUIRED: Find the work done on the spring.


    2. Relevant equations
    Solution 1 uses: W = ΔE, & (elastic energy} Ee = 0.5(k)x2, where k is the constant, and x is displacement from equilibrium position.

    Solution 2 uses: W = F(Δd), & (elastic/spring force} Fe = kx, where k is the constant, and x is the displacement from the equilibrium position.


    3. The attempt at a solution
    Please evaluate these solutions & choose the best. Please tell me why. Please correct my misunderstandings. Thanks!

    SOLUTION 1.
    w = ΔE
    w = Eefinal - Eeinitial
    w = 0.5(k)xfinal2 - 0 {because initial the spring is at the eq. position.)
    w = 0.5(170N/m)(0.1m)2
    w = 0.85J

    SOLUTION 2.
    w = F(Δd)
    w = Fe(Δd)
    w = kx(Δd)
    w = (170N/m)(0.1m)(0.1m)
    w = 1.7J


    Which solution is better, and why? (It's obvious why the values are different.)
    Please help me understand why/where these approaches are best. (I understand calculus, but I need to understand these concepts, before I use calculus to evaluate.)
     
  2. jcsd
  3. Jun 11, 2013 #2

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    The second method is wrong, F is not constant during the displacement.
     
  4. Jun 11, 2013 #3
    Thanks very much! ! !

    Is there a resource you can point me to that explains why the force is not constant? Or, can you tell me why?

    I'm not trying to be difficult, I just want to understand. I really want to be an engineer.
     
  5. Jun 11, 2013 #4

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    Just check how you calculated the force at 10cm excitation. What is the force at an excitation of 5cm?
     
  6. Jun 11, 2013 #5
    (elastic/spring force} Fe = kx, displacement x varies.Hence force is not constant
     
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: Best solution? for work done on a spring.
  1. Work Done by Spring (Replies: 3)

  2. Work done by a spring (Replies: 6)

Loading...