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Homework Help: What is the Force Constant k of a Spring?

  1. Oct 29, 2013 #1
    1. The problem statement, all variables and given/known data

    A 4.50 ✕ 10^5 kg subway train is brought to a stop from a speed of 0.500 m/s in 0.900 m by a large spring bumper at the end of its track. What is the force constant k of the spring?

    M- 4.50E5 kg
    IV- .5m/s
    FV- 0m/s

    2. Relevant equations
    PE = (.5)kx^2

    3. The attempt at a solution
    k=(450000kg)(9.81m/s^2)/ .9 = 4900000, which isn't the right answer. Can someone help me out?
    Last edited: Oct 29, 2013
  2. jcsd
  3. Oct 29, 2013 #2
    Have you read anything about the concept of potential energy of a spring?This question is directly based on that..
    The kinetic energy of the train is being converted in the potential energy of spring?
  4. Oct 29, 2013 #3
    Well I know PE = (.5)kx^2, but Im afraid I don't know how to plug in the numbers.
  5. Oct 29, 2013 #4
    What's the intial kinetic energy (KE) of the train?
    KE will = 0 when v = 0 (why is this true?)
    Due to conservation of potential energy, initial(KE+PE) = final(KE+ E)
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