Re: [Phys-L] f'(t) / g'(t) question

[Richard Tarara <rtarara@saintmarys.edu>]

Unless I'm missing something here, g'(t)/f'(t) is just 
vy/vx--dimensionless and fairly useless. Think of the extremes--vertical 
motion the value is zero, horizontal the value is undefined (or 
infinite).  Sure vx^2 + vy^2 = v^2, but that is a different relationship.

rwt

On 4/8/2016 9:52 AM, Lulai, Paul wrote:
> Hi.
> I haven't really used my calculus for quite some time.  I was asked by a
> math department colleague the following:
> if  x=f(t) and y = g(t) then dx/dt = f'(t) and dy/dt = g'(t) would be
> velocity vectors.
> so far so good.
>
> The question:
> is g'(t) / f'(t)  a velocity value? can it be used to determine
> instantaneous velocity values?
>
> My knee-jerk response is that it is not a velocity value. However, i don't
> know if there is a way to use this to find the instantaneous velocity. I am
> pretty-much brain-locked into x' ^2 + y'^2 = v^2 when dealing with just
> kinematics.
>
> Is there a useful or common thing that is appropriate here?
>
> Thanks for your time.
>
> Paul Lulai
> Physics Teacher
> St Anthony Village Senior High
> St Anthony Village MN 55418
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Richard Tarara
Professor Emeritus
Saint Mary's College

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