# Homework Help: Springs are considered a non-conservative force why is the

1. Oct 18, 2011

### mrshappy0

1. The problem statement, all variables and given/known data
Quick conceptual questions:

Is springs are considered a non-conservative force why is the mechanical energy conserved when a moving object compresses the spring?

2. Relevant equations

3. The attempt at a solution

This isn't a homework question or anything but I working on a problem that involves a spring and the problem says that a mass horizontally attached to a spring is moving compressed by a bullet being shot into the mass (wood) and that the mechanical energy is conserved during the compression of the spring. Confused.

Last edited by a moderator: Oct 18, 2011
2. Oct 18, 2011

### Staff: Mentor

Re: Springs

Who said that the spring force is non-conservative?

3. Oct 18, 2011

### mrshappy0

Re: Springs

Hmm... Wow.. People troll to much. hah.. So it is conservative.

4. Oct 18, 2011

### Staff: Mentor

Re: Springs

Sure, a spring force is conservative. That's why you can have a spring potential energy function.

But be careful with that 'bullet getting shot into the wood' problem. While the spring compression is conservative, the initial collision of bullet and wood does not conserve kinetic energy: it's an inelastic collision.

5. Oct 18, 2011

### mrshappy0

Re: Springs

Right. Potential energy is conserved in inelastic collisions. This allows the use of the potential energy = kinetic energy. THanks Doc!

6. Oct 18, 2011

### Staff: Mentor

Re: Springs

Not exactly! What's conserved in an inelastic collision (and all collisions, actually) is momentum.

7. Oct 18, 2011

### mrshappy0

Oops I meant momentum. Slipped up on my words. To many new concepts flopping around in my word recall section in my brain.