# Simple Harmonic Easy Qualitve problem, something I'm not getting

1. Feb 19, 2015

### Jediknight

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

Which of these forces could result in simple harmonic motion

F(x)=−9(x−7)3

F(x)=−9x+7

F(x)=−9x3

F(x)=−9x

F(x)=9x
F(x)=9x3

9x3 is 9x^3, same with itsopposite
2. Relevant equations

F=kx, the definition of shm

3. The attempt at a solution

I figured -9x and 9x were the only ones, i tried that

i tried those two and 9x+7 might work, just a measurement from a different spot

then I tried taking off -9x (leaving 9x and 9x+7) out of despiration

I'm thinking maybe its a trick question and the answer might be all of them (like how pendulum at very small distances can be looked at as smh, or is there some fundamental concept I'm not getting here?

2. Feb 19, 2015

### Staff: Mentor

Check the sign on your equation above that I've bolded in red. That's not the traditional definition used with Hooke's Law: http://en.wikipedia.org/wiki/Hooke's_law

3. Feb 19, 2015

### Jediknight

good call, if F equaled kx a spring would push a load further and faster til it hit the speed of light!

(incase it wasnt obvious to everyone reading, F=-kx, F=-kx+c is fine to