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Re: PSE Example 8.6 via Reduce

  • To: mathgroup at smc.vnet.net
  • Subject: [mg112865] Re: PSE Example 8.6 via Reduce
  • From: Eduardo Cavazos <wayo.cavazos at gmail.com>
  • Date: Mon, 4 Oct 2010 06:05:29 -0400 (EDT)
  • References: <i7mq41$ovh$1@smc.vnet.net>

On Sep 26, 1:44 am, Eduardo  Cavazos <wayo.cava... at gmail.com> wrote:

> Here's example 8.6 from PSE [1]:
>
>    http://i.imgur.com/HJLqs.png
>
> Here I'll be working with the "exercise" portion of the example; i.e.
> the case where there is friction between point A and point B.
>
> Use Reduce on the set of equations which describe the system between
> point A and point B:
>
>    http://i.imgur.com/PLWza.png
>
> The result shows that vB is about 12.9.
>
> Now use Reduce on the set of equations which describe the system
> between point B and point C. Also, plug in our value of 'vB' manually:
>
>    http://i.imgur.com/rujUz.png
>
> We get the correct answer for dBC; i.e. about 40.3.
>
> Above I solved the problem in "piecemeal" fashion; first I used Reduce
> on the system from A to B and used the result from that to work with
> the system from B to C, also using Reduce.
>
> I don't have alot of experience with Reduce, but it seems like, in
> theory, I should be able to throw the whole set of equations at Reduce
> in one step, instead of in two steps. However, when I try to do so,
> Mathematica seems to have trouble with it (at least on this system;
> Pentium M with about 1.5GB RAM). So something along the lines of:
>
>    http://i.imgur.com/2swfE.png
>
> So my questions are... Is this too much for Reduce to handle? Would
> you recommend the piecemeal method instead?

In particular, the trouble is that the computation ran over 3 hours
without completing. When I split up the problem, each piece takes a
few seconds.

Ed


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