# Re: Physics help (I found it!)

```Kelly wrote:
>>Well thats part of it. It certainly doesn't give me a warm comfident
>>feeling when our numbers are that far apart! Eiather we're talking about
>>something fundamentally different and don't realize it, one of us has a
>>blown calculator, or one of us is badly misappling some equation.

Was that you?

>We were both talking about something fundamentally differnt, but didn't
>know it!  The difference was all due to the slightly different Delta V.
>The Exponential makes a hellish difference given even slight differnces in
>the speed assumptions.
>
>(See why I always want to see examples with numbers and units with your
>equations Tim?)

The numbers where there before, but apparently they did not help much.

>So a 55 to 1 fuel ratio with a Vexh of 2E7 m/s:
>
>55 = exp (?/2E7)
>
>or
>
>2e7 * Ln (55) = 80E6  = .267c
>
>So we can still get a burn down from over 1/4th c with the same fuel ratio.
>Giving a touch under 17 years for a flight time to Alpha C.  Much better
>than I was afraid of.

That mass ratio is only for acceleration OR deceleration, if you want to do
both you need to square that mass ratio. (55^2=3025)

Isn't AC a bit too close?

Timothy

```