- #1

Dorothy Weglend

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An air glider is attached to a massless spring, which is compressed 0.18 m from it's relaxed position. Find the velocity of the glider at its original position, and at 0.25 m. Spring constant is 10 N/m, mass of glider is 0.15 kg.

I have solved this problem, but I am having trouble understanding the potential energy issues for the distance of 0.25 m. The first is easy:

kx^2/2 = mv^2/2

The second is also not difficult:

kx^2/2 = mv^2/2 + k(0.25-0.18)^2/2

But I do not really "get" this second equation. I understand that the massless spring can't have any kinetic energy, since k = mv^2/2, and it is massless, then k-0 when the spring is at its original position, and I think that would be the highest speed.

But as it continues past that point, it must build up a potential energy. But I don't know how to think about this. There must be some energy somewhere that is being converted into potential energy, but if there is truly no kinetic energy, where is the potential energy of the spring coming from? I can't believe it is coming from the glider, that makes no sense, but there is nothing else that is doing anything here.

If someone could help me understand this, I would be so grateful.

Thanks,

Dorothy