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