# Energy stored in a spring

## Homework Statement

How much energy can be stored in a spring with k = 400N/m if the maximum possible stretch is 12cm?

U = 1/2k(x^2)

## The Attempt at a Solution

I tried using the above equation. U = 1/2(400)(.12^2) = 2.88.

This looks correct, what's your question exactly?

If I'm not mistaken, that's the energy of just one particle from the spring.

Astronuc
Staff Emeritus
The mechanical energy is stored uniformly in the spring for the most part (assuming uniform material properties, e.g. elastic modulus), but that is the energy that would be imparted to any mass at the end of the spring (with respect to the other end) if the spring were released and pushed or pulled the mass.

Well I tried the answer, and it was wrong. I don't know what other equation I would use.

PhanthomJay
Homework Helper
Gold Member
Well I tried the answer, and it was wrong. I don't know what other equation I would use.
what units should you use for the stored energy? (You left them out).

It would be (N/m)(m^2) = Nm = J

PhanthomJay
Homework Helper
Gold Member
It would be (N/m)(m^2) = Nm = J
OK try 2.88J or 2.9J (I'm not good at significant figures) and see if the computer buys it.

As far as sig figs go, I think it should be 3 Joules. We only know the spring constant to one significant digit.

PhanthomJay
Homework Helper
Gold Member
As far as sig figs go, I think it should be 3 Joules. We only know the spring constant to one significant digit.
Yes, I think you're right, webassign gets very picky.

Holy crap everyone!! I am so sorry about this problem. I was just going to try entering 3, when I noticed that I didn't put the decimal point into my original answer. BIG difference between 288 and 2.88! Sorry again!!!!!

PhanthomJay