# 2nd Diff eq application - Vertical stretch

1. Aug 10, 2016

### Arij

Hello guys,
first I am sorry I didn't use the template. I deleted it by mistake and I didn't know how to create a new thread from scratch.

so I have two cases of the same problem, on with initial conditions of pulling down and the other pushing up, I tried different signs but It didn't work. Can anyone explain to me the difference in dealing with this?

thank you

2. Aug 11, 2016

### BvU

Hi,
Bit difficult to help here. I take it this is a computerized teaching situation and you did well on the picture on the left (I don't see the green shading, though). And not so well on the right. Is that correct ?
If so, I notice you use the two roots on the left, but not on the right. Could you type your work that leads you to $2e^{-x}$ ?

3. Aug 11, 2016

### BvU

You can simply recover the template by starting a new thread and then cut the template from the new thread and paste it in the existing one. Then not post the new thread.

Looked at your work (as if I have plenty of time to do so...) and found you made a very simple mistake. I don't blame you but I blame your computerized workbook for three reasons:
1. choosing y+ as 'down' is unhealthy
2. working in the cgs system is very unhealthy
3. a spring that stretches 1.11 m when 2 gram weight is appended is weird
If you write down your two equations for the initial conditions you'll see your mistake right away .

Last edited: Aug 11, 2016
4. Aug 11, 2016

### BvU

Oh, and what is the independent variable ? x ?

 skip my last tip in #3; you did enter -2 at first, I can assume.