speediest inclined plane
We set the problem, how great must be the difference in altitude of the top and the bottom of an inclined plane in that a little ball would frictionlessly roll the whole length of the plane as soon as possible
(cf. the brachistochrone problem (http://planetmath.org/CalculusOfVariations)). It is assumed that the http://planetmath.org/node/9475projection of the length on a horizontal plane has a given value b.
Using notations of mechanics, we can write
F=ma=mgsinα=mgx√x2+b2, |
√x2+b2=s=12t2a=t22⋅gx√x2+b2. |
Thus we get the function
t2=2g⋅x2+b2x=:f(x) |
the absolute minimum point of which is to be found. This function is differentiable, and its derivative
is
The only zero of is , where the sign changes from minus to plus as increases. It means that is the searched minimum point. The difference in altitude is thus equal to the http://planetmath.org/node/11642base, and the inclination must be .
Title | speediest inclined plane |
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Canonical name | SpeediestInclinedPlane |
Date of creation | 2013-03-22 19:19:11 |
Last modified on | 2013-03-22 19:19:11 |
Owner | pahio (2872) |
Last modified by | pahio (2872) |
Numerical id | 9 |
Author | pahio (2872) |
Entry type | Example |
Classification | msc 26A09 |
Classification | msc 26A06 |
Related topic | Extremum![]() |
Related topic | CalculusOfVariations |
Related topic | BrachistochroneCurve |