# RE: 400N P3D Rocket

```> >At the risk of embarrasing myself, here's my calculated:
> >(snip)
>
> Exactly right. It's high school physics (Newton's 2nd Law,
> f = ma). I don't see why it's viewed as mysterious.
> Especially in a supposedly technically-savvy group like
> this one.
>
> Missing yet another deep and mysterious point, I suppose...

:-)  Normally, one would say "not exactly rocket science", but this is the
very principle of rockets. :)

While we're on a roll, let's see how long it takes to do the 1/4 mile.  I'll
be a bit metric, for the sake of simplicity, and do the calculation over 400
metres (which is within 10' of a real 1/4 mile).

>From previous calculations, we know:

u (initial speed) = 0 m/s
a = 400/115 = 3.478 m/s^2

s = ut + 1/2at^2

For a standing start, this (u=0), this simplifies to:

s = 1/2 at^2

Solving for t, gives

t = sqrt (2s/a)

Substituting the values

t = sqrt (2 x 400 / 3.478)

t = sqrt (230), = 15.165 seconds

Not quite a dragster. :-)
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