# Energy stored in a spring

1. Oct 31, 2007

### aligass2004

1. The problem statement, all variables and given/known data

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

2. Relevant equations

U = 1/2k(x^2)

3. The attempt at a solution

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

2. Oct 31, 2007

### hotcommodity

This looks correct, what's your question exactly?

3. Nov 1, 2007

### dzogi

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

4. Nov 1, 2007

### Staff: Mentor

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.

5. Nov 1, 2007

### aligass2004

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

6. Nov 1, 2007

### PhanthomJay

what units should you use for the stored energy? (You left them out).

7. Nov 1, 2007

### aligass2004

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

8. Nov 1, 2007

### PhanthomJay

OK try 2.88J or 2.9J (I'm not good at significant figures) and see if the computer buys it.

9. Nov 1, 2007

### hotcommodity

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

10. Nov 1, 2007

### PhanthomJay

Yes, I think you're right, webassign gets very picky.

11. Nov 2, 2007

### aligass2004

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!!!!!

12. Nov 2, 2007

### PhanthomJay

Great, just when I learn how to do significant figures, the computer wasn't looking for 'em. That figures!