The maximum length that a spring can stretch in reality

[Edel Crine]

Homework Statement

Is it possible to stretch a spring about 400m from its rest position in reality?

Relevant Equations

F=-kx

In detail, I came up with 424m for the stretched length of a spring in order to change the mass of an object by 10^-9kg which originally was 1 kg. Problem said, "is it feasible?"
In my opinion, there is no spring that can be stretched for this long, so it is not feasible. However, I'm not sure whether is it possible or not...

 

[berkeman]

Homework Statement:: Is it possible to stretch a spring about 400m from its rest position in reality?
Relevant Equations:: F=-kx

In detail, I came up with 424m for the stretched length of a spring in order to change the mass of an object by 10^-9kg which originally was 1 kg.

Sorry, this makes no sense to me. Mass of what object? What mechanism is causing the mass to change? Can you show your detailed calculations that result in 424m?

And if a coil spring has a diameter of 800m, it probably can be stretched out 400m without any plastic deformation. What a strange question, IMO...

 

[Edel Crine]

Sorry, this makes no sense to me. Mass of what object? What mechanism is causing the mass to change? Can you show your detailed calculations that result in 424m?

And if a coil spring has a diameter of 800m, it probably can be stretched out 400m without any plastic deformation. What a strange question, IMO...

My bad! So the question would be, a 1-kg mass attached horizontally to a spring with constant k = 1000N/m. How much should I stretch it to change the mass of this spring-mass system by 10^-9 kg? Is it feasible?

So I used the formula for change in potential energy,
ΔE = ΔmC^2 = (10^-9kg)(3*10^8m/s) = 9*10^7 J.
In this problem, ΔE = ΔU = 0.5k(xf^2-xi^2)-0.5k(xi), but xi is 0, so it would be:
ΔE = ΔU = 0.5k(xf)^2.
xf = √(2ΔE/k) = 424.26 m.
Therefore, the spring should be stretched by 424.26m in order to change its mass to 10^-9kg.
This is my work so far and I am not sure whether is it feasible or not...