Wednesday, March 17, 2010

A railroad track runs absolutely straight and level for exactly one mile?

Assume that the two ends are fixed but that the track expands by one foot and buckles up in the shape of an arc of a Parabola. How far is the middle of that arc off of the ground?


Please provide a detailed explaination, I would be very grateful:)

A railroad track runs absolutely straight and level for exactly one mile?
5280 feet in a mile, so we can write the parabola as y=-a*(x+2640) *(x-2640), i.e., put the endpoints at x-intercepts (+/- 2640,0) and vertex of the upside down parabola at (0, 2640^2*a). Then integrate the arclength sqrt(1+y'^2) from x= -2640 to x=2640 to get a messy transcendental expression, then solve this equal to 5281 (one foot extra track) to get a=.6385012467 *10^-5 approximately. Then the y-intercept (ht of track) is 2640^2*a which is about 44.50098289 or 44.5 feet up.
Reply:It will be 50ft from the ground.



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