       Re: need help determined time to travel a path

• To: mathgroup at smc.vnet.net
• Subject: [mg107528] Re: need help determined time to travel a path
• From: Narasimham <mathma18 at hotmail.com>
• Date: Tue, 16 Feb 2010 03:51:44 -0500 (EST)
• References: <hlb8oj\$rk0\$1@smc.vnet.net>

```You assumed that a frictionless particle rotates with uniform angular
velocity in the x - y vertical plane under action of gravity, leading
to unnatural results. Also value of acceleration due to gravity is to
be supplied, pi should be Pi and quantities under radical sign to be
checked  positive.

On Feb 15, 3:47 pm, "bwal... at musings.com" <brad2... at gmail.com> wrote:
> I am trying to determine the time to travel a circular path. This path is on a
> circle. It's fairly easy to understand.
>
> But, I can't seem to figure out why this is failing.
>
> (* define my parametrizations *)
> circlex[t_]:=13+13*Sin[t+pi];
> circley[t_]:=13+13*Cos[t+pi];
>
> (* the derivatives *)
> dcirx[t_]:=D[circlex[t],t];
> dciry[t_]:=D[circley[t],t];
>
> (* amount of time needed to travel a circle *)
> Integrate[Sqrt[(dcirx[t])^2+(dciry[t])^2]/Sqrt[2*g*(circley[time0]-
> circley[t])], {t, 0.01, pi/2}]
>
> I get a negative value for the time. This can't be right..
>
> Any help is much appreciated!!
>
> Thanks.
>