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2 spring questions-

  1. Oct 30, 2012 #1
    Question 1:

    1. The problem statement, all variables and given/known data
    You have a spring at height d where it is relaxed.
    You drop a ball (mass m) from a height (h) so that it lands on the spring with spring constant k.
    What is the max compression of the spring in terms of given variables?
    Given-

    m
    g
    k
    d
    h


    2. Relevant equations
    Find
    dmax=max compression distance

    3. The attempt at a solution
    i did-

    deltaUgrav+deltaUspring=0

    (mg(d-dmax)-mg(d+h))+(.5k(dmax)^2-.5k(d-d))=0

    mgd-mgdmax-mgd-mgh+.5k(dmax)^2=0

    -mg(dmax)-mg(h)+.5k(dmax)^2=0

    .5k(dmax)^2=mg(dmax+h)

    Can you solve for dmax or do u have to do quadratic equation?


    Question 2:

    1. The problem statement, all variables and given/known data
    If you have a spring and an object with mass m
    and you put the object on the spring and let go, without giving it any initial velocity, what is the work done by the spring on the object? Answer is symbolic
    Given variables-

    Fspring with respect to s
    m
    g
    k
    s0(= initial length, relaxed length)
    sf
    2. Relevant equations

    Symbollically, what is the work done?

    3. The attempt at a solution

    I did it like this-

    Work= Integral(Fspring) evaluated from initial s to final s

    so

    Integral of ks ds= .5ks^2] sf-s0

    =.5k(sf)^2-.5k(s0)^2
    =.5k(sf-s0)

    Is this the right amount of work?
     
    Last edited: Oct 30, 2012
  2. jcsd
  3. Oct 30, 2012 #2

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    It is almost impossible to read what you have written. Calculate the kinetic energy and potential energy the weight has when it hits the spring (take the floor as 0 potential energy so I think you mean the natural length of the spring). Find the work done to compress the spring a distance x and the potential energy at height d- x. Set the total energy at each height equal and solve for x.
     
  4. Oct 30, 2012 #3
    Ok let me change things to be more readable
     
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