Re: First order linear diff eq in a word problem.

From: D (moi_at_e-dan.net)
Date: 06/29/04 

Date: 29 Jun 2004 14:11:28 -0700

moi@e-dan.net (D) wrote in message news:<1f28a65f.0406281057.774bfa70@posting.google.com>...
> A homework problem was encountered this weekend that left me stumped.
> I'm hoping someone with a strong Diff Eq history can help solve this
> mystery. The source:
>
> 12686 = 16t - 116.3 * e^(-2t) + 116.3
>
> I need to solve for 't' such that t = time. I'm stumped here (yes, I
> did subtract 116.3 to the other side. Just showing the problem in its
> form). No worries though, for I've turned in the assignment. Perhaps
> someone will be nice enough to give the solution so I don't rip my
> hair out over the frustration of this. If the entire problem is
> required, I won't hesitate to place an addendum later. Thanks in
> advance.
>
> Daniel Lausevic

Thanks for the replies people. Last night, I opted to use a TI-89 and
it came out with the same results: Around 13 minutes (785.60625
seconds). The problem was a Diff Eq problem involving a person
jumping from an airplane at an initial altitude of 15000 ft.
Calculating the time it takes to touch the ground was the final
question. Otherwise it was two sets of initial value problems, as you
may imagine. The final equation, was related to the final time it
took to touch the ground minus the initial freefall time. I don't use
calculators so I was stumped. William is correct by saying the 'w
identities' aren't included in math textbooks. When I located a
similar problem in another textbook, it had a computer icon next to
it. Since my book didn't have that included, I assumed it was to be
solved without a computer algebra system. Either way, thanks for the
help.