# Energy in a Spring Question

1. Oct 15, 2007

### shotgunbob

1. The problem statement, all variables and given/known data
A .3 kg mass rest on top of a spring that has been compressed by .04 m. Neglect any frictional effects, and consider the spring to be massless. Then, if the spring has a constant k equal to 2000 n/m, to what height will the mass rise when the system is released.

2. Relevant equations

PE(spring)= (1/2)kx^2

KE= 1/2mv^2

3. The attempt at a solution

I got the PE in the system to be 1.6 J. Im not sure how this would translate into a vertical height. Thanks in advance!

Last edited: Oct 15, 2007
2. Oct 15, 2007

### Staff: Mentor

How did you arrive at this?

Consider gravitational PE.

3. Oct 15, 2007

### shotgunbob

I messed up, used PE=1/2kmx^2 for some reason. I got 1.6 J.

And in Grav. PE, the H should be the same as the H Im looking for so PE(grav)=PE(Spring).
Or maybe Im missing something.

4. Oct 15, 2007

### shotgunbob

Ok I got .54 m when i put Pe(grave)=Pe(spring). Thats an answer choice! Is this correct?

5. Oct 15, 2007

### Staff: Mentor

It depends on what the height is being measured with respect to. The initial position on top of the spring? Or the compressed position?

6. Oct 15, 2007

### shotgunbob

I suppose its the top of the spring

7. Oct 15, 2007

### Staff: Mentor

That's what I would say.

8. Oct 15, 2007

Thank you!