# Homework Help: Mass on a spring(SHM)

1. Apr 7, 2010

### anti404

1. The problem statement, all variables and given/known data
A mass attached to a holder hangs from a spring. the combined mass of the hanger, spring, and mass=45g. Adding mass of 55g stretches the spring 12cm. What is the spring constant?

2. Relevant equations
Hooke's Law
F=kx

3. The attempt at a solution
(m1+m2)g/x=k
(.045kg+.055kg)9.8m/s^2/m = k
but this isn't right, I don't think.

I'm not sure what I'm missing, but it seems that I don't have all the information correctly utilized. Hooke's law, though, is the only thing I could think to use with the given information and based upon what we need to find.
any help would be greatly appreciated, as I need this information for my laboratory experiment.

2. Apr 8, 2010

### inutard

The mass of the spring do not need to be used as stretching with 55g stretches from the equilibrium state (the equilibrium state holes the 45g from the spring and system)

3. Apr 8, 2010

### anti404

okay, so the mass of the spring etc. isn't used, and mg/x=K=4.49N/m.
then to find the period of oscillation when ALL masses are attached, T=2pi[sqroot(m/k)].
now when it says all the masses are attached, would you still not include the spring? I'm confused because it says something about having the spring adjusted 1/3 or something for its mass.

thanks,
Justin

4. Apr 9, 2010

### inutard

Your work looks right. The mass for the period should be 55g.