# Homework Help: Force done by the spring if a weight is attached

1. Oct 13, 2011

### dav1d

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

What is the force done by the spring if an object of mass m is attached.

2. Relevant equations
F=ma
F=-kx
Fg=mg

3. The attempt at a solution

Sum F = 0
mg-kx=0
mg-Fs=0
Fs=mg

Therefore the force done by the spring is mg? is the +/- right? for direction? Is the force right?

2. Oct 13, 2011

### Morphheus

The mass is hanging from the spring. I assume that when it is observed, it can be considered at rest.
If it's at rest, there are only two forces acting on the mass: gravity and the spring force. Since the mass is at rest, all forces must cancel eachother.
.
Since both forces are acting in opposite directions, they shouldn't have the same sign.

You stated that Sum F = 0. Therefore, Fs + Fg = 0

3. Oct 13, 2011

### dav1d

Ok so then Fs=-Fg=-mg.
Just change the sign of my answer?

4. Oct 13, 2011

### Morphheus

Yep.

5. Oct 13, 2011

### dav1d

ok thank you very much!! i thought the sign was a bit messed up.