Originally Posted by

**Wilmer** Had another look...above is incorrect (sorry Earboth!); should be:

s = 2 - (v+10)(v-10) / 2g

This leads to your v^2 = 4g + 100 - 2gs : so you made no typo!

You want help in getting to above, right? Well, let's see:

s = -g/2[(10-v)/g]^2 + 10[(10-v)/g] + 2 : that's what we start with, ok?

Multiply by -2:

-2s = g[(10-v)/g]^2 - **20[(10-v)**/g] - 4 : changes -g/2 to g (easier!)

Expand:

-2s = g[(100 - 20v + v^2) / g^2] - **(200 + 20v)** / g - 4 **<--- are you sure?**

Multiply by g:

-2gs = 100 - 20v + v^2 - 200 + 20v - 4g

Simplify:

-2gs = v^2 - 100 - 4g

In terms of v^2:

v^2 = 4g + 100 - 2gs : SUCCESS!!

By the way, that was my way of doing it; there are other ways...