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Homework Help: Determine the compression of the spring

  1. Mar 20, 2015 #1
    1. The problem statement, all variables and given/known data

    Russian aviator Vsevolod Mikhailovich Abramovich invented the Abramovich Flyer based on the design of the Wright brothers' first plane. After this first success, Abramovich became obsessed with deep space travel designing a spring based launcher to fire a probe of mass 90kg from Earth (mass 6.00×10^24kg, radius 6.40×10^6m) into deep space.

    Determine the minimum speed to launch this probe into deep space such that it never returns.

    vesc= 11183.1346 m/s

    Determine the compression of the spring, having spring constant 5.50×105N[PLAIN]https://s3.lite.msu.edu/adm/jsMath/fonts/cmmi10/alpha/144/char3D.pngm, [Broken] needed to launch this probe using Abramovich's design.


    2. Relevant equations


    F⃗ spring=−kŝ


    3. The attempt at a solution

    First part I just plugged it into the V escape equation.

    Second part attempt: 5.50×10^5N[PLAIN]https://s3.lite.msu.edu/adm/jsMath/fonts/cmmi10/alpha/144/char3D.pngm [Broken] * 6.40×10^6m = 3.52E12 Newtons

    3.52E12 =

    U = mc^2
    U = 6E24*(3E8)^2 = 5.41E41

    Integrate (1/2)(5.50×10^5N[PLAIN]https://s3.lite.msu.edu/adm/jsMath/fonts/cmmi10/alpha/144/char3D.pngm [Broken])^2 - 5.41E41

    Maybe use Youngs Module to find compression?

    I think I'm somewhere on the right track but I'm kinda lost..
    Last edited by a moderator: May 7, 2017
  2. jcsd
  3. Mar 20, 2015 #2


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    Staff: Mentor

    Have you considered a straight forward conservation of energy approach? What's the KE required for the probe to escape?
  4. Mar 20, 2015 #3
    KE = (1/2)mv^2
    KE = (1/2) (90kg) (11183.1346)^2

    Would I use that answer to then multiply it by the given stiffness?
  5. Mar 20, 2015 #4


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    Staff: Mentor

    Not quite. You'd want to make sue that your spring, when compressed, is storing at least that much energy so that when it relaxes it imparts that much energy to the probe. What's the expression for the PE stored in a compressed spring?

    You might also want to convince yourself that the gravitational PE change for the probe through the spring's relaxation distance is not a significant contributor to the calculation.
  6. Mar 20, 2015 #5

    Integrating this equation once would give us the Potential Energy that was obtained.

    My second attempt:
    Set KE=(1/2)mv^2 and -W=(1/2)kx^2 equal to each other

    Solve for x

  7. Mar 21, 2015 #6


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    Staff: Mentor

    That result looks good.
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